MAINTAINERS: add S390 MM section

Alexander Gordeev and Gerald Schaefer are covering the whole s390 specific
memory management code. Reflect that by adding a new S390 MM section to
MAINTAINERS.

Also rename the S390 section to S390 ARCHITECTURE to be a bit more precise.
Acked-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

MAINTAINERS

@@ -17987,7 +17987,7 @@ L:	linux-fbdev@vger.kernel.org
 S:	Maintained
 F:	drivers/video/fbdev/savage/
 
-S390
+S390 ARCHITECTURE
 M:	Heiko Carstens <hca@linux.ibm.com>
 M:	Vasily Gorbik <gor@linux.ibm.com>
 M:	Alexander Gordeev <agordeev@linux.ibm.com>
@@ -18042,6 +18042,15 @@ L:	netdev@vger.kernel.org
 S:	Supported
 F:	drivers/s390/net/
 
+S390 MM
+M:	Alexander Gordeev <agordeev@linux.ibm.com>
+M:	Gerald Schaefer <gerald.schaefer@linux.ibm.com>
+L:	linux-s390@vger.kernel.org
+S:	Supported
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git
+F:	arch/s390/include/asm/pgtable.h
+F:	arch/s390/mm
+
 S390 PCI SUBSYSTEM
 M:	Niklas Schnelle <schnelle@linux.ibm.com>
 M:	Gerald Schaefer <gerald.schaefer@linux.ibm.com>