Platforms/RaspberryPi: SMBIOS Type 4 fixes

Various fixes and enhancements for SMBIOS Type 4:
 - Fix ProcessorId to correctly report the Arm64 MIDR_EL1 value
 - Change ProcessorUpgrade from Other to None
 - Add comments for ProcessorCharacteristics fields
 - Add CoreCount2, EnabledCoreCount2, and ThreadCount2
 - Set LxCacheHandle to 0xFFFF

Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Pete Batard <pete@akeo.ie>
Cc: Andrei Warkentin <awarkentin@vmware.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Samer El-Haj-Mahmoud <samer.el-haj-mahmoud@arm.com>
Reviewed-by: Andrei Warkentin <awarkentin@vmware.com>