virt: acrn: Introduce interfaces for MMIO device passthrough

virt: acrn: Introduce interfaces for MMIO device passthrough

MMIO device passthrough enables an OS in a virtual machine to directly
access a MMIO device in the host. It promises almost the native
performance, which is required in performance-critical scenarios of
ACRN.

HSM provides the following ioctls:
  - Assign - ACRN_IOCTL_ASSIGN_MMIODEV
    Pass data struct acrn_mmiodev from userspace to the hypervisor, and
    inform the hypervisor to assign a MMIO device to a User VM.

  - De-assign - ACRN_IOCTL_DEASSIGN_PCIDEV
    Pass data struct acrn_mmiodev from userspace to the hypervisor, and
    inform the hypervisor to de-assign a MMIO device from a User VM.

These new APIs will be used by user space code vm_assign_mmiodev and
vm_deassign_mmiodev in
https://github.com/projectacrn/acrn-hypervisor/blob/master/devicemodel/core/vmmapi.c

Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Signed-off-by: Fei Li <fei1.li@intel.com>
Link: https://lore.kernel.org/r/20210923084128.18902-2-fei1.li@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>