MdePkg: MmConfiguration: Move definition of EFI_MM_RESERVED_MMRAM_REGION

MdePkg: MmConfiguration: Move definition of EFI_MM_RESERVED_MMRAM_REGION

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3440

The definition of EFI_MM_RESERVED_MMRAM_REGION, according to PI Spec 1.5
is also referenced in EFI_PEI_MM_CONFIGURATION_PPI. Defining this
structure as is will enforce any potential usage of MM Configuration PPI
interface to include <Protocol/MmConfiguration.h>.

This change moves this structure definition to PiMultiPhase.h, which is
already included by Protocol/MmConfiguration.h through PiMmCis.h. It also
paves way for introducing Ppi/MmConfiguration.h with proper dependency.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Kun Qin <kuqin12@gmail.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>