OMAP2/3 CM: clean up 3430ES2-only defines

This patch marks several CM register bit fields that are only valid on
3430ES2 and beyond to be 3430ES2 defines.

While we're here, clean up the register defines in cm.h, and improve
documentation slightly.  Also, since CM_AUTOIDLE3 is now in use on
both OMAP24xx and OMAP34xx, remove the platform-specific prefix from
its name.

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