sunxi: enable MMU_PGPROT proper page table protection

Select the new MMU_PGPROT Kconfig symbol for all Allwinner board builds,
to use a write-protected .rodata, non-executable .data and .rodata
sections, and non-writable .text sections.

This might trigger runtime exceptions in misbehaving drivers, which
should then be fixed.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>

arch/arm/Kconfig

@@ -1190,6 +1190,7 @@ config ARCH_SUNXI
 	select DM_SPI_FLASH if SPI && MTD
 	select DM_KEYBOARD
 	select DM_SERIAL
+	select MMU_PGPROT if ARM64
 	select OF_BOARD_SETUP
 	select OF_CONTROL
 	select PINCTRL