dcmi: implement get sensor info

This commit implements the plumbing around the 'Get Sensor
Info' command. It doesn't read the sensor information yet.
That code is coming up in a subsequent commit.

Refactor some of the get temperature readings code, in order to reuse
certain common aspects for this commit.

Change-Id: I0cb531b5b75e98cc9e76509f84f832be9997fee0
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/host-ipmid-whitelist.conf b/host-ipmid-whitelist.conf
index 0c9c382..97544a0 100644
--- a/host-ipmid-whitelist.conf
+++ b/host-ipmid-whitelist.conf
@@ -31,4 +31,5 @@
 0x2C:0x02    //<Group Extension>:<Get Power Reading>
 0x2C:0x03    //<Group Extension>:<Get Power Limit>
 0x2C:0x06    //<Group Extension>:<Get Asset Tag>
+0x2C:0x07    //<Group Extension>:<Get Sensor Info>
 0x2C:0x10    //<Group Extension>:<Get Temperature Readings>