build/Sgi: Add Firmware Version Support

The firmware version number string appears as "EDK II" in SMBIOS type 0
record which is not meaningful. In order to have meaningful value which
indicates release version of firmware,introduce a variable to hold the
value of release version of firmware.

This variable will be later used in edk2-platform code to contruct the
smbios type 0 record.

Signed-off-by: Dishendra Deshmukh <dishendra.deshmukh@arm.com>
Change-Id: I867eec3120c83bdbc78ef9c3dd410fd125d4aa21