KVM: SVM: Add support for expedited writes to the fast MMIO bus

KVM: SVM: Add support for expedited writes to the fast MMIO bus

Wire up SVM's #NPF handler to fast MMIO.  While SVM doesn't provide a
dedicated exit reason, it's trivial to key off PFERR_RSVD_MASK.  Like VMX,
restrict the fast path to L1 to avoid having to deal with nGPA=>GPA
translations.

For simplicity, use the fast path if and only if the next RIP is known.
While KVM could utilize EMULTYPE_SKIP, doing so would require additional
logic to deal with SEV guests, e.g. to go down the slow path if the
instruction buffer is empty.  All modern CPUs support next RIP, and in
practice the next RIP will be available for any guest fast path.

Copy+paste the kvm_io_bus_write() + trace_kvm_fast_mmio() logic even
though KVM would ideally provide a small helper, as such a helper would
need to either be a macro or non-inline to avoid including trace.h in a
header (trace.h must not be included by x86.c prior to CREATE_TRACE_POINTS
being defined).

Link: https://patch.msgid.link/20251113221642.1673023-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>