VMCI: dma dg: add MMIO access to registers

VMCI: dma dg: add MMIO access to registers

Detect the support for MMIO access through examination of the length
of the region requested in BAR1. If it is 256KB, the VMCI device
supports MMIO access to registers.

If MMIO access is supported, map the area of the region used for
MMIO access (64KB size at offset 128KB).

Add wrapper functions for accessing 32 bit register accesses through
either MMIO or IO ports based on device configuration.

Sending and receiving datagrams through iowrite8_rep/ioread8_rep is
left unchanged for now, and will be addressed in a later change.

Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Signed-off-by: Jorgen Hansen <jhansen@vmware.com>
Link: https://lore.kernel.org/r/20220207102725.2742-3-jhansen@vmware.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>