OvmfPkg: resolve DebugAgentLib for DXE_SMM_DRIVER modules

OvmfPkg: resolve DebugAgentLib for DXE_SMM_DRIVER modules

Add mappings to DebugAgentLib for SMM modules to prevent build breaks when
SMM_REQUIRE and SOURCE_DEBUG_ENABLE are both set.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
[lersek@redhat.com: cover the X64 dsc, update commit msg, kudos Jordan]
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19051 6f19259b-4bc3-4df7-8a09-765794883524