clk: versatile/icst: add Integrator core module clocks

The Integrator/AP and Integrator/CP have special derivatives
of the ICST525 control registers, where some bits have been
hardwired but others are possible to adjust, resulting in a
control register that makes it possible to set an even,
desired megahertz value.

The Integrator/AP and Integrator/CP have slightly different
layout so we support them using different compatible
strings.

After adding these clocks, the Integrator-specific cpufreq
driver can be switched over to use the generic operating
point device tree cpufreq driver.

Instead of simply writing a value to the oscillator control
register we switch to the more elaborate method of providing
a bitmask and use regmap_update_bits() to poke the right bits
for the desired frequency, this is needed since these control
registers sometimes control more than one clock.

Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>