MdePkg/Library/UefiDevicePathLib: Add back StandaloneMm INF file

MdePkg/Library/UefiDevicePathLib: Add back StandaloneMm INF file

REF: https://github.com/tianocore/edk2/pull/3130

The above PR removed UefiDevicePathLibStandaloneMm.inf, which is
a non-backwards compatible change and does not provide time for
downstream platforms to use the UefiDevicePathLibBase.inf.

Add UefiDevicePathLibStandaloneMm.inf back, but add comments that
it is deprecated and that UefiDevicePathLibBase.inf should be used
instead.

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Cc: Mateusz Albecki <mateusz.albecki@intel.com>
Cc: Yanbo Huang <yanbo.huang@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>