UefiCpuPkg/MpInitLib: Set the SW exit fields when performing VMGEXIT

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3008

All fields that are set in the GHCB should have their associated bit in
the GHCB ValidBitmap field set. Add support to set the bits for the
software exit information fields when performing a VMGEXIT (SwExitCode,
SwExitInfo1, SwExitInfo2).

Fixes: 20da7ca42a33d3ef767ce4129f11496af7f67c9f
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Acked-by: Ray Ni <ray.ni@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <6e11dd7e161bddeacc3fb4817467cef24510c31c.1604685192.git.thomas.lendacky@amd.com>