KVM: SVM: Convert plain error code numbers to defines

Convert VMGEXIT SW_EXITINFO1 codes from plain numbers to proper defines.

Opportunistically update the comment for the malformed input "sub-error"
codes to state that they are defined by the GHCB, and to capure the
relationship to the malformed input response.

No functional change intended.

Signed-off-by: Melody Wang <huibo.wang@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Pavan Kumar Paluri <papaluri@amd.com>
Link: https://lore.kernel.org/r/20250225213937.2471419-2-huibo.wang@amd.com


[sean: update comments]
Signed-off-by: Sean Christopherson <seanjc@google.com>