ARM: imx6q: resume PL310 only when CACHE_L2X0 defined

Original patch from Lothar Waßmann, this patch fixes a building error
when CONFIG_CACHE_L2X0 is not defined.

Cc: Lothar Waßmann <lw@karo-electronics.de>
Signed-off-by: Eric Miao <eric.miao@linaro.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>