KVM: x86/mmu: Account pf_{fixed,emulate,spurious} in callers of "do page fault"

Move the accounting of the result of kvm_mmu_do_page_fault() to its
callers, as only pf_fixed is common to guest page faults and async #PFs,
and upcoming support KVM_PRE_FAULT_MEMORY won't bump _any_ stats.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>