ARM: imx_v6_v7_defconfig: Enable VPU driver

Let VPU driver be selected by default.

VPU driver requires a SRAM pool, so select CONFIG_SRAM as well.

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