KVM: x86: Consolidate SEV-ES MMIO emulation into a single public API

KVM: x86: Consolidate SEV-ES MMIO emulation into a single public API

Dedup kvm_sev_es_mmio_{read,write}() into a single API, as the "cost" of
plumbing in a boolean is largely negligible since KVM pulls out a boolean
for ops->write anyways, and consolidating the APIs will allow for
additional cleanups.

No functional change intended.

Tested-by: Tom Lendacky <thomas.lendacky@gmail.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Link: https://patch.msgid.link/20260225012049.920665-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>