s390x: mmu: add support for large pages

Add support for 1M and 2G pages.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@de.ibm.com>
Message-Id: <20210611140705.553307-7-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>