Implement GetPLDMVersion command

This commit implements the GetPLDMVersion which is required
as part of the base PLDM support to know the version of a
given PLDM type.

Change-Id: I1bcbd938c5b6833f62e0ee2f474b04d76b6970d9
Signed-off-by: Sampa Misra <sampmisr@in.ibm.com>