MdePkg/Register/Amd: define GHCB macros for SNP AP creation
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275
    
    Version 2 of GHCB introduces NAE for creating AP when SEV-SNP is enabled
    in the guest VM. See the GHCB specification, Table 5 "List of Supported
    Non-Automatic Events" and sections 4.1.9 and 4.3.2, for further details.
    
    While at it, define the VMSA state save area that is required for creating
    the AP. The save area format is defined in AMD APM volume 2, Table B-4
    (there is a mistake in the table that defines the size of the reserved
    area at offset 0xc8 as a dword, when it is actually a word). The format of
    the save area segment registers is further defined in AMD APM volume 2,
    sections 10 and 15.5.
    
    Cc: James Bottomley <jejb@linux.ibm.com>
    Cc: Min Xu <min.m.xu@intel.com>
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Cc: Tom Lendacky <thomas.lendacky@amd.com>
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Cc: Erdem Aktas <erdemaktas@google.com>
    Cc: Michael D Kinney <michael.d.kinney@intel.com>
    Cc: Liming Gao <gaoliming@byosoft.com.cn>
    Cc: Zhiguang Liu <zhiguang.liu@intel.com>
    Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    Message-Id: <20210519181949.6574-7-brijesh.singh@amd.com>
    [lersek@redhat.com: fix typo in BZ reference]