ARM: 9247/1: mm: set readonly for MT_MEMORY_RO with ARM_LPAE

MT_MEMORY_RO is introduced by commit 598f0a99 ("ARM: 9210/1:
Mark the FDT_FIXED sections as shareable"), which is a readonly
memory type for FDT area, but there are some different between
ARM_LPAE and non-ARM_LPAE, we need to setup PMD_SECT_AP2 and
L_PMD_SECT_RDONLY for MT_MEMORY_RO when ARM_LAPE enabled.

non-ARM_LPAE	0xff800000-0xffa00000           2M PGD KERNEL      ro NX SHD
ARM_LPAE	0xff800000-0xffc00000           4M PMD RW NX SHD
ARM_LPAE+fix	0xff800000-0xffc00000           4M PMD ro NX SHD

Fixes: 598f0a99

 ("ARM: 9210/1: Mark the FDT_FIXED sections as shareable")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>