sched, numa, mm, s390/thp: Implement pmd_pgprot() for s390

sched, numa, mm, s390/thp: Implement pmd_pgprot() for s390

This patch adds an implementation of pmd_pgprot() for s390,
in preparation to future THP changes.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>