powerpc/mm: Refactor the floor/ceiling check in hugetlb range freeing functions

All hugetlb range freeing functions have a verification like the following,
which only differs by the mask used, depending on the page table level.

	start &= MASK;
	if (start < floor)
		return;
	if (ceiling) {
		ceiling &= MASK;
		if (! ceiling)
			return;
		}
	if (end - 1 > ceiling - 1)
		return;

Refactor that into a helper function which takes the mask as
an argument, returning true when [start;end[ is not fully
contained inside [floor;ceiling[

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/16a571bb32eb6e8cd44bda484c8d81cd8a25e6d7.1604668827.git.christophe.leroy@csgroup.eu