MpInitLib: Put SEV logic in separate file

MpInitLib: Put SEV logic in separate file

The patch does several simplifications:
1. Treat SwitchToRealProc as part of RendezvousFunnelProc.
   So the common logic in MpLib.c doesn't need to be aware of
   SwitchToRealProc.
   As a result, SwitchToRealSize/Offset are removed from
   MP_ASSEMBLY_ADDRESS_MAP.

2. Move SwitchToRealProc to AmdSev.nasm.
   All other assembly code in AmdSev.nasm is called through
   OneTimeCall.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>