[at91] Save power by disabling the processor clock when CPU is idle

[avictor.za at gmail.com]

> Disable the processor clock when the CPU is idle.
>
> This saves much more power than merely entering 'Wait for Interrupt' mode.
> Since JTAG-debugging doesn't work when the processor clock is switched off,
> make it conditional on CONFIG_DEBUG_KERNEL.
>
> Signed-off-by: Anders Larsen <al at alarsen.net>
> Cc: Andrew Victor <avictor.za at gmail.com>

Acked-by: Andrew Victor <linux at maxim.org.za>

Russell:  It is patch 6053/1 in the patch-system.