OvmfPkg: Fix Xcode assembly issue

OvmfPkg: Fix Xcode assembly issue

The Xcode assembler is much pickier than GCC. Also the 64-bit
linker is not a fan of relocations so it is better to us IP
relative code, but at least it removes a relocation entry.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Andrew Fish <afish@apple.com>
[jordan.l.justen@intel.com: use .byte for retfq rather than lret]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14055 6f19259b-4bc3-4df7-8a09-765794883524