ANDROID: x86/paravirt: Add pv_mmio_ops

Add pv_mmio_ops in the paravirt to support PV MMIO instruction various.
By default, the MMIO ops in pv_ops are initialized by the native MMIO
instruction various. A virtual platform kernel can overwrite these MMIO
ops by its own PV methods.

Bug: 391539939
Bug: 353950489
Test: Microdroid works as a protected VM
Upstream-Task: 402758258

Change-Id: I7cfff97792953e983929aeebfdabcf20e6bdc383
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Signed-off-by: Dmytro Maluka <dmaluka@google.com>