ARM: 8693/1: discard memblock arrays when possible

On ARM the generic pfn_valid() version is used with some configurations
such as SA1100 based devices. In that case the memblock arrays are no
longer used after boot and can be discarded.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>

arch/arm/Kconfig

@@ -2,6 +2,7 @@ config ARM
 	bool
 	default y
 	select ARCH_CLOCKSOURCE_DATA
+	select ARCH_DISCARD_MEMBLOCK if !HAVE_ARCH_PFN_VALID
 	select ARCH_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE