[ARM] 3785/1: S3C2412: Fix idle code as default uses wrong clocks

Patch from Ben Dooks

Fix the idle code on the s3c2412 as the default
code is using bits in the CLKCON register that are
no-longer there.

Provide an override for the idle code, and ensure
that the power configuration is set to allow idle
instead of stop or sleep.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>