KVM: x86: de-underscorify __emulator_pio_in

Now all callers except emulator_pio_in_emulated are using
__emulator_pio_in/complete_emulator_pio_in explicitly.
Move the "either copy the result or attempt PIO" logic in
emulator_pio_in_emulated, and rename __emulator_pio_in to
just emulator_pio_in.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>