ANDROID: pkvm: introduce memory mapped I/O emulation framework

Introduce a new data structure pkvm_mmio_emul_table to store MMIO handler.
Add a helper function to register MMIO handler into the emulation table.
Define host_mmio_emul_table for host MMIO emulation.

Signed-off-by: Tinghao Zhang <tinghao.zhang@intel.com>

Bug: 349990461
Test: Android can run protected VMs

Change-Id: I6a52354927d3e294427d331d5699c5fbc84b1d40
Signed-off-by: Dmytro Maluka <dmaluka@google.com>