convert map_domain_page_global() to using mfn_t

convert map_domain_page_global() to using mfn_t

The sh_map/unmap wrappers can be dropped, and take the opportunity to turn
some #define's into static inlines, for added type saftey.

As part of adding the type safety, GCC highlights an problematic include cycle
with arm/mm.h including domain_page.h which includes xen/mm.h and falls over
__page_to_mfn being used before being declared.  Simply dropping the inclusion
of domain_page.h fixes the compilation issue.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>