ARM: at91: at91_dt_defconfig: remove CC_OPTIMIZE_FOR_SIZE

Use the default optimization level for the kernel, build with
the "-O2" which corresponds to CC_OPTIMIZE_FOR_PERFORMANCE.

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>

Author: cristibirsan

arch/arm/configs/at91_dt_defconfig

@@ -6,7 +6,6 @@ CONFIG_LOG_BUF_SHIFT=16
 CONFIG_CGROUPS=y
 CONFIG_CGROUP_CPUACCT=y
 CONFIG_BLK_DEV_INITRD=y
-CONFIG_CC_OPTIMIZE_FOR_SIZE=y
 CONFIG_EMBEDDED=y
 CONFIG_SLAB=y
 CONFIG_ARCH_MULTI_V4T=y