powerpc/8xx: DEBUG_PAGEALLOC doesn't require an ITLB miss exception handler

Since commit e611939f ("powerpc/mm: Ensure change_page_attr()
doesn't invalidate pinned TLBs"), pinned TLBs are not anymore
invalidated by __kernel_map_pages() when CONFIG_DEBUG_PAGEALLOC is
selected.

Remove the dependency on CONFIG_DEBUG_PAGEALLOC.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e796c5fcb5898de827c803cf1ab8ba1d7a5d4b76.1606231483.git.christophe.leroy@csgroup.eu