microblaze: switch to generic version of pte allocation

microblaze: switch to generic version of pte allocation

The microblaze implementation of pte_alloc_one() has a provision to
allocated PTEs from high memory, but neither CONFIG_HIGHPTE nor pte_map*()
versions for suitable for HIGHPTE are defined.

Except that, microblaze version of pte_alloc_one() is identical to the
generic one as well as the implementations of pte_free() and
pte_free_kernel().

Switch microblaze to use the generic versions of these functions.  Also
remove pte_free_slow() that is not referenced anywhere in the code.

Link: http://lkml.kernel.org/r/1565690952-32158-1-git-send-email-rppt@linux.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>