ARM: imx6: remove __CPUINIT annotation from v7_invalidate_l1

The recent suspend testing on !SMP build discovers that the __CPUINIT
annotation for v7_invalidate_l1 should not be there, as the function
is called by resume path for not only SMP but also !SMP build.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>