ARM: OMAP2+: clock: use driver API instead of direct memory read/write

Clock nodes shall use the services provided by underlying drivers to access
the hardware registers instead of direct memory read/write. Thus, change
all the code to use the new omap2_clk_readl / omap2_clk_writel APIs for this.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>