KVM: SVM: Drop 32-bit "support" from __svm_sev_es_vcpu_run()

KVM: SVM: Drop 32-bit "support" from __svm_sev_es_vcpu_run()

Drop 32-bit "support" from __svm_sev_es_vcpu_run(), as SEV/SEV-ES firmly
64-bit only.  The "support" was purely the result of bad copy+paste from
__svm_vcpu_run(), which in turn was slightly less bad copy+paste from
__vmx_vcpu_run().

Opportunistically convert to unadulterated register accesses so that it's
easier (but still not easy) to follow which registers hold what arguments,
and when.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240223204233.3337324-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>