StandaloneMmPkg: Remove dependency on ArmPlatformPkg.dec
    
    Bugzilla: 3150 (https://bugzilla.tianocore.org/show_bug.cgi?id=3150)
    
    Update StandaloneMmCoreEntryPoint to remove the unnecessary
    dependency on ArmPlatformPkg.dec.
    
    Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
    Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
    Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>