ShellPkg UefiDpLib: Use Image->FilePath to get name for SMM drivers

This enhancement is to use the FilePath field in the loaded image
protocol to find the name of an image as a fallback for when the
loaded image device path protocol is not installed on the image handle.
This is necessary because the SMM core does not install the loaded
image device path protocol, so DP was displaying "Unknown Driver Name"
for every SMM driver.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Shumin Qiu <shumin.qiu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19683 6f19259b-4bc3-4df7-8a09-765794883524