[ARM] 3578/1: AT91RM9200 Clock update

Patch from Andrew Victor

Some updates to the clock infrastructure for the AT91RM9200.

1. Hard-coded values replaced with names defined in at91rm9200_sys.h.
2. Added the four PIO clocks, which are enabled at startup.
3. At startup, disable all unused clocks.
4. Minor bugfix for usage counts associated with MCK. [Patch from David
Brownell]
5. Added at91_clock_associate() function to associate device & function
with a particular clock.  [Patch from David Brownell]

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>