ARM: mxs_defconfig: Add mx23evk and mx28evk build

The patch adds following configurations to enable build of mx23evk
and mx28evk in defconfig.

  CONFIG_MACH_MX23EVK
  CONFIG_MACH_MX28EVK
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/configs/mxs_defconfig

@@ -22,6 +22,8 @@ CONFIG_BLK_DEV_INTEGRITY=y
 # CONFIG_IOSCHED_DEADLINE is not set
 # CONFIG_IOSCHED_CFQ is not set
 CONFIG_ARCH_MXS=y
+CONFIG_MACH_MX23EVK=y
+CONFIG_MACH_MX28EVK=y
 CONFIG_MACH_STMP378X_DEVB=y
 CONFIG_MACH_TX28=y
 # CONFIG_ARM_THUMB is not set