virt: sev-guest: Contain snp_guest_request_ioctl in sev-guest

SNP Guest Request uses only exitinfo2 which is a return value from GHCB, has
meaning beyond ioctl and therefore belongs to struct snp_guest_req.

Move exitinfo2 there and remove snp_guest_request_ioctl from the SEV platform
code.

No functional change intended.

Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Dionna Glaze <dionnaglaze@google.com>
Link: https://lore.kernel.org/20250611040842.2667262-2-aik@amd.com