xen/arm: gnttab: use static inlines for gnttab_{release_}host_mapping*

xen/arm: gnttab: use static inlines for gnttab_{release_}host_mapping*

Function unmap_common_complete (common/grant_table.c) defines and sets
a variable ld that is later on passed to a macro:
gnttab_host_mapping_get_page_type().
On Arm this macro does not make use of any arguments causing a compiler
to warn about unused-but-set variable (when -Wunused-but-set-variable
is enabled). Fix it by converting this macro to a static inline
helper and using the boolean return type.

While there, also convert macro gnttab_release_host_mappings.

Signed-off-by: Michal Orzel <michal.orzel@arm.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>