omap2 clock: move 24xx clock definitions from clock.h into clock24xx.h

In preparation for OMAP34xx clock definitions, move OMAP24xx-specific
struct clks and prcm_config into a new file, 'clock24xx.h'.  Also correct
several style infelicities that checkpatch complains about.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>