ARM: imx_v6_v7_defconfig: Select CONFIG_TOUCHSCREEN_EGALAX

egalax touchscren controller is present on mx6 sabresd/sabrelite, so let's
enable it by default.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>