It turns out that all platforms using the ICST VCO are really
just touching two registers, and in the same way as well: one
register with the VCO configuration as such, and one lock register
that makes it possible to write to the VCO.

Factor this register read/write into the ICST driver so we can
reuse it in the IM-PD1 driver.
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NMike Turquette <mturquette@linaro.org>

The ICST307 VCO clock has a shared driver in the ARM
architecture. This patch provides a wrapper into the common
clock framework so we can use the implementation in the
ARM architecture without duplicating the code until all
ARM platforms using this VCO are moved over. At that point
we can merge the driver from the ARM platform into the
generic file altogether.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Mike Turquette <mturquette@ti.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
[mturquette@linaro.org: removed versatile Kconfig]
Signed-off-by: NMike Turquette <mturquette@linaro.org>