Patch from Ben Dooks

Move to using an enable count for the shared clocks
and protect the clock system using a mutex instead
of just disabling IRQs during the clock update.

Since there is little more code in the path for
non-shared clocks, the enable and disable calls
use the same code for each.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>