ARM: imx_v6_v7_defconfig: Select CONFIG_PERF_EVENTS

Select CONFIG_PERF_EVENTS so that oprofile can be used.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Dirk Behme <dirk.behme@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>