bm_instance: Create a new handler

This OEM handler will get properties from tmpfs to serve over IPMI.

Tested:
~# cat /run/bm-instance/asset-tag
12345
~# ipmitool raw 0x2e 0x32 0x79 0x2b 0x00 0x17 0x00
 79 2b 00 17 05 31 32 33 34 35
...
...
(Verified this works for all 7 sub commands)

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: I191b6f4994d91ada49a3332a8e93a3a305561904
diff --git a/commands.hpp b/commands.hpp
index cc22a23..0dc80e6 100644
--- a/commands.hpp
+++ b/commands.hpp
@@ -67,6 +67,8 @@
     SysGetAccelVrSettings = 21,
     // Google CustomAccel Set VR Settings
     SysSetAccelVrSettings = 22,
+    // Get BM instance property info
+    SysGetBMInstanceProperty = 23,
 };
 
 } // namespace ipmi