ARM: highbank: select ARCH_HAS_HOLES_MEMORYMODEL

On Midway, the first 4G of memory starts at 0 and the rest of memory
(4GB+) starts at 0x2_00000000, so we need to enable pfn_valid checks
by selecting ARCH_HAS_HOLES_MEMORYMODEL.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

arch/arm/mach-highbank/Kconfig

 config ARCH_HIGHBANK
 	bool "Calxeda ECX-1000/2000 (Highbank/Midway)" if ARCH_MULTI_V7
 	select ARCH_HAS_CPUFREQ
+	select ARCH_HAS_HOLES_MEMORYMODEL
 	select ARCH_HAS_OPP
 	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select ARM_AMBA