KVM: SVM: Allow SNP guest policy to specify SINGLE_SOCKET

KVM: SVM: Allow SNP guest policy to specify SINGLE_SOCKET

KVM currently returns -EINVAL when it attempts to create an SNP guest if
the SINGLE_SOCKET guest policy bit is set. The reason for this action is
that KVM would need specific support (SNP_ACTIVATE_EX command support) to
achieve this when running on a system with more than one socket. However,
the SEV firmware will make the proper check and return POLICY_FAILURE
during SNP_ACTIVATE if the single socket guest policy bit is set and the
system has more than one socket:

 - System with one socket
   - Guest policy SINGLE_SOCKET == 0 ==> SNP_ACTIVATE succeeds
   - Guest policy SINGLE_SOCKET == 1 ==> SNP_ACTIVATE succeeds

 - System with more than one socket
   - Guest policy SINGLE_SOCKET == 0 ==> SNP_ACTIVATE succeeds
   - Guest policy SINGLE_SOCKET == 1 ==> SNP_ACTIVATE fails with
     POLICY_FAILURE

Remove the check for the SINGLE_SOCKET policy bit from snp_launch_start()
and allow the firmware to perform the proper checking.

This does have the effect of allowing an SNP guest with the SINGLE_SOCKET
policy bit set to run on a single socket system, but fail when run on a
system with more than one socket. However, this should not affect existing
SNP guests as setting the SINGLE_SOCKET policy bit is not allowed today.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/4c51018dd3e4f2c543935134d2c4f47076f109f6.1748553480.git.thomas.lendacky@amd.com
Signed-off-by: Sean Christopherson <seanjc@google.com>