ARM: socfpga_defconfig: Enable HIGHMEM

All of the SoCFPGA boards have at least 1GB of RAM, so enabling HIGHMEM
is necessary to avoid the following warning:

[    0.000000] Truncating RAM at 0x00000000-0x40000000 to -0x30000000
[    0.000000] Consider using a HIGHMEM enabled kernel.
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>

arch/arm/configs/socfpga_defconfig

@@ -25,6 +25,7 @@ CONFIG_PCIE_ALTERA_MSI=y
 CONFIG_SMP=y
 CONFIG_NR_CPUS=2
 CONFIG_AEABI=y
+CONFIG_HIGHMEM=y
 CONFIG_ZBOOT_ROM_TEXT=0x0
 CONFIG_ZBOOT_ROM_BSS=0x0
 CONFIG_VFP=y