KVM: x86: add read_phys to x86_emulate_ops

We want to read the physical memory when emulating RSM.

X86EMUL_IO_NEEDED is returned on all errors for consistency with other
helpers.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>