xen/common: move the memory_mapping DOMCTL hypercall to common code

xen/common: move the memory_mapping DOMCTL hypercall to common code

This commit moves to common code the implementation of the memory_mapping
DOMCTL, currently available only for the x86 architecture. It also adds
a definition for the PADDR_BITS constant for ARM, that is to be used in
common code and currently not available for the ARM architecture.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Acked-by: Jan Beulich <JBeulich@suse.com>
Acked-by: Julien Grall <julien.grall@citrix.com>
Tested-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: Ian Campbell <Ian.Campbell@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>