p2m: move p2m-common.h inclusion point

p2m: move p2m-common.h inclusion point

The header is (hence its name) supposed to be a helper for the per-arch
p2m.h files. It was never supposed to be included directly, and for the
purpose of putting common function declarations into the common header
it is more helpful if things like p2m_t are already available at the
inclusion point.

This also undoes parts of 02ede7dc03 ("memory: add
check_get_page_from_gfn() as a wrapper..."), which had been there just
because of the unhelpful original way of including p2m-common.h.

Take the opportunity and also ditch a duplicate public/memory.h from the
ARM header.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>