arm/imx: fix cpufreq section mismatch

WARNING: arch/arm/plat-mxc/built-in.o(.data+0x488): Section mismatch in reference from the variable mxc_driver to the function .init.text:mxc_cpufreq_init()
The variable mxc_driver references
the function __init mxc_cpufreq_init()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>