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

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