x86/sev: Require the RMPREAD instruction after Zen4

Limit usage of the non-architectural RMP format to Zen3/Zen4 processors.
The RMPREAD instruction, with architectural defined output, is available
and should be used for RMP access beyond Zen4.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Reviewed-by: Ashish Kalra <ashish.kalra@amd.com>
Link: https://lore.kernel.org/r/5be0093e091778a151266ea853352f62f838eb99.1733172653.git.thomas.lendacky@amd.com