clk: versatile/icst: support for AP baseboard clocks

This adds support for the two ICST525-based clocks on the
Integrator/AP baseboard, as documented in the board manual
"Integrator/AP ASIC Development Motherboard", ARM DUI0098 B,
pages 3-15 thru 3-18.

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