ARM: imx: enable imx6q-cpufreq support

Update operating-points per hardware document and add support for
1 GHz and 1.2 GHz frequencies.

400 MHz, 800 MHz and 1 GHz should be supported by all i.MX6Q chips,
while 1.2 GHz support needs to know from OTP fuse bit.

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