omap2 clock: drop RATE_CKCTL from all OMAP2 clocks

RATE_CKCTL is no longer meaningful in the OMAP2 clock framework, so, drop it
from all clocks.  We keep the flag around since it's still used by OMAP1.

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