libpldm: Add APIs to decode descriptor entries

PLDM firmware update package header has record descriptors with type,
length and value. The response of QueryDeviceIdentifiers command has
the same format. This patch provides the decode API to iterate the
descriptor entries and also to parse the vendor defined descriptor
value.

The descriptor identifier table is based of DSP0267_1.1.0. The
implementation is compatible with the earlier verions DSP0267_1.0.0
and DSP0267_1.0.1.

Tested: Unit tests passed

Signed-off-by: Tom Joseph <rushtotom@gmail.com>
Change-Id: I900d190db3248068dbe93090ce646fd63ec957eb
diff --git a/libpldm/utils.h b/libpldm/utils.h
index 1e15e18..3011a5a 100644
--- a/libpldm/utils.h
+++ b/libpldm/utils.h
@@ -12,7 +12,7 @@
 
 /** @struct variable_field
  *
- *  Structure representing variable filed in the pldm message
+ *  Structure representing variable field in the pldm message
  */
 struct variable_field {
 	const uint8_t *ptr;