arch/arm: add consistency check to REMOVE p2m changes

arch/arm: add consistency check to REMOVE p2m changes

Currently, the REMOVE case of the switch in apply_p2m_changes()
does not perform any consistency check on the mapping to be removed.
More in detail, the code does not check if the guest address to be
unmapped is actually mapped to the machine address given as a
parameter.
This commit adds the above-described consistency check to the REMOVE
path of apply_p2m_changes() and lets a warning be emitted when trying
to remove a non-existent mapping. This is instrumental to one of the
following commits, which implements the possibility to trigger the
removal of p2m ranges via the memory_mapping DOMCTL for ARM.

Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Julien Grall <julien.grall@citrix.com>
Cc: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Paolo Valente <paolo.valente@unimore.it>
Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>
Cc: Jan Beulich <JBeulich@suse.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>
Acked-by: Ian Campbell <ian.campbell@citrix.com>