mmc: Add update-bios-attr-table subcommand

Add the update-bios-attr-table subcommand to update the bios attribute
table with the host firmware well-known names based on system type. The
system type is provided by Entity Manager, and this new subcommand uses
some of the existing infrastructure that the process-host-firmware
subcommand has to determine the system type.

Add a new service file to run this new subcommand so that it can block
waiting for the entity manager interface to appear on D-Bus.

Subsequent commands will add parsing the JSON file to build the bios
attribute string and set the bios attribute property.

Change-Id: Iacee975e273bae562d2d42cd8b642b9d0744a121
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meson.build b/meson.build
index 1b654b2..aa2ce5a 100644
--- a/meson.build
+++ b/meson.build
@@ -125,6 +125,7 @@
         'mmc/obmc-flash-bios-init.service',
         'mmc/obmc-flash-bios-patch.service',
         'mmc/openpower-process-host-firmware.service',
+        'mmc/openpower-update-bios-attr-table.service',
     ]
 endif