ARM: i.MX remove last leftovers from legacy clock support

This also removes mach/clock.h along the way

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mike Turquette <mturquette@linaro.org>