xen/x86: factor out map and unmap from the memory_mapping DOMCTL

xen/x86: factor out map and unmap from the memory_mapping DOMCTL

This commit factors out from the XEN_DOMCTL_memory_mapping hypercall
implementation, currently available only for x86, the operations
related to memory ranges map and unmap. The code is factored out
into two {map|unmap}_mmio_regions() functions for x86, that will match
the corresponding pair of ARM functions when the DOMCTL will be moved
to common code in the following commit. This commit also adds an
unmap_mmio_regions() function for ARM so that the following transition
to common code is cleaner.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Acked-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
Acked-by: Jan Beulich <JBeulich@suse.com>
Acked-by: Julien Grall <julien.grall@citrix.com>
Cc: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Paolo Valente <paolo.valente@unimore.it>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Eric Trudeau <etrudeau@broadcom.com>
Cc: Viktor Kleinik <viktor.kleinik@globallogic.com>
Cc: Andrii Tseglytskyi <andrii.tseglytskyi@globallogic.com>