[ARM] 5438/1: AT91: manage clock by functionality instead of CPUs

In clock.c file the clock management is grouped by cpu with cpu_is_xxx()
function. This lead to some kind of difficulties to read this file and
maintainability issues as the number of AT91 cpus & PLLs/clocks is growing.

In this patch, I try to group clock functionality together and match cpus with
this functionality set.
An update to at91_pmc.h is needed to cover some new PMC possibilities (and
some update in comments).

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Andrew Victor <avictor.za@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>