x86/sev: Use the SVSM to create a vCPU when not in VMPL0

Using the RMPADJUST instruction, the VMSA attribute can only be changed
at VMPL0. An SVSM will be present when running at VMPL1 or a lower
privilege level.

In that case, use the SVSM_CORE_CREATE_VCPU call or the
SVSM_CORE_DESTROY_VCPU call to perform VMSA attribute changes. Use the
VMPL level supplied by the SVSM for the VMSA when starting the AP.

  [ bp: Fix typo + touchups. ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/bcdd95ecabe9723673b9693c7f1533a2b8f17781.1717600736.git.thomas.lendacky@amd.com