PrmPkg: Replace PcdPrmPlatformGuid with EDKII_DSC_PLATFORM_GUID

PrmPkg: Replace PcdPrmPlatformGuid with EDKII_DSC_PLATFORM_GUID

Bugzilla request https://bugzilla.tianocore.org/show_bug.cgi?id=2969
was recently completed which causes the PLATFORM_GUID value from the
DSC file to be placed into Autogen file .c & .h files. With this
change, the PRM Platform GUID can be directly matched to the DSC
PLATFORM_GUID value.

Cc: Andrew Fish <afish@apple.com>
Cc: Kang Gao <kang.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Benjamin You <benjamin.you@intel.com>
Cc: Liu Yun <yun.y.liu@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Acked-by: Liming Gao <gaoliming@byosoft.com.cn>
Acked-by: Leif Lindholm <quic_llindhol@quicinc.com>
Reviewed-by: Ankit Sinha <ankit.sinha@intel.com>