cpufreq: imx6q: read OCOTP through nvmem for imx6ul/imx6ull

cpufreq: imx6q: read OCOTP through nvmem for imx6ul/imx6ull

commit 2733fb0d0699246711cf622e0e2faf02a05b69dc upstream.

On i.MX6UL/i.MX6ULL, accessing OCOTP directly is wrong because
the ocotp clock needs to be enabled first. Add support for reading
OCOTP through the nvmem API, and keep the old method there to
support old dtb.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>