[ARM] 4913/1: [AT91] PMC_MDIV definitions

The allowed values for the MDIV field (Master Clock Division) in the
PMC controller differ between the AT91RM9200 and AT91SAM9/CAP9.
To remove possible confusion, change the definitions to be more explicit.

Also define the Processor Clock Division bits.

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