xen/ioreq: Make x86's hvm_mmio_first(last)_byte() common

xen/ioreq: Make x86's hvm_mmio_first(last)_byte() common

The IOREQ is a common feature now and these helpers will be used
on Arm as is. Move them to xen/ioreq.h and replace "hvm" prefixes
with "ioreq".

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
CC: Julien Grall <julien.grall@arm.com>
[On Arm only]
Tested-by: Wei Chen <Wei.Chen@arm.com>