nvmes: add Availability interface

Add Availability interface.
When PwrGoodPin is low, Set Available property to false to indicate
this sensor is currently unavilable due to power loss.

Tested on Bletchley:

- PwrGoodPin is low
root@bletchley:~# busctl introspect xyz.openbmc_project.nvme.manager \
> /xyz/openbmc_project/sensors/temperature/nvme6 \
> xyz.openbmc_project.Sensor.Value
NAME                             TYPE      SIGNATURE RESULT/VALUE                             FLAGS
.MaxValue                        property  d         127                                      emits-change writable
.MinValue                        property  d         -127                                     emits-change writable
.Unit                            property  s         "xyz.openbmc_project.Sensor.Value.Uni... emits-change writable
.Value                           property  d         -127                                     emits-change writable
root@bletchley:~# busctl introspect xyz.openbmc_project.nvme.manager \
> /xyz/openbmc_project/sensors/temperature/nvme6 \
> xyz.openbmc_project.State.Decorator.Availability
NAME                                             TYPE      SIGNATURE RESULT/VALUE FLAGS
.Available                                       property  b         false        emits-change writable

- PwrGoodPin is high
root@bletchley:~# busctl introspect xyz.openbmc_project.nvme.manager \
> /xyz/openbmc_project/sensors/temperature/nvme6 \
> xyz.openbmc_project.Sensor.Value
NAME                             TYPE      SIGNATURE RESULT/VALUE                             FLAGS
.MaxValue                        property  d         127                                      emits-change writable
.MinValue                        property  d         -127                                     emits-change writable
.Unit                            property  s         "xyz.openbmc_project.Sensor.Value.Uni... emits-change writable
.Value                           property  d         33                                       emits-change writable
root@bletchley:~# busctl introspect xyz.openbmc_project.nvme.manager \
> /xyz/openbmc_project/sensors/temperature/nvme6 \
> xyz.openbmc_project.State.Decorator.Availability
NAME                                             TYPE      SIGNATURE RESULT/VALUE FLAGS
.Available                                       property  b         true         emits-change writable

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Change-Id: I0b621ae619dde85607c635912c7230bbe9de22ac
diff --git a/nvme_manager.cpp b/nvme_manager.cpp
index cdb76b1..51b0f7d 100644
--- a/nvme_manager.cpp
+++ b/nvme_manager.cpp
@@ -617,6 +617,7 @@
                                     : IS_PRESENT;
         auto pwrGoodPinValStr =
             (config.pwrGoodPin) ? getGPIOValueOfNvme(devPwrGoodPath) : POWERGD;
+        const bool isPwrGood = (pwrGoodPinValStr == POWERGD);
 
         if (presentPinValStr != IS_PRESENT)
         {
@@ -636,7 +637,7 @@
             continue;
         }
 
-        if (pwrGoodPinValStr != POWERGD)
+        if (!isPwrGood)
         {
             // IFDET should be used to provide the final say
             // in SSD's presence - IFDET showing SSD is present
@@ -672,6 +673,7 @@
         // (To make thermal loop know that the sensor reading
         //  is invalid).
         readNvmeData(config);
+        nvmes.find(config.index)->second->setSensorAvailability(isPwrGood);
     }
 }
 } // namespace nvme