StandaloneMmPkg: Add library files to DSC

StandaloneMmPkg: Add library files to DSC

Bugzilla: 3150 (https://bugzilla.tianocore.org/show_bug.cgi?id=3150)

The Core CI reports a critical error if the library files are
not included in the DSC.

Therefore, add the missing library files to the package DSC.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>