OvmfPkg: add DXE_DRIVER for providing TSEG-as-SMRAM during boot-time DXE

OvmfPkg: add DXE_DRIVER for providing TSEG-as-SMRAM during boot-time DXE

The SMM core depends on EFI_SMM_ACCESS2_PROTOCOL. This small driver (which
is a thin wrapper around "OvmfPkg/SmmAccess/SmramInternal.c" that was
added in the previous patch) provides that protocol.

Notably, EFI_SMM_ACCESS2_PROTOCOL is for boot time only, therefore
our MODULE_TYPE is not DXE_RUNTIME_DRIVER.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19041 6f19259b-4bc3-4df7-8a09-765794883524