[ARM] 5264/2: [AT91] Suspend-to-RAM disables main oscillator

This patch adds support for a low(er)-power suspend-to-RAM.
In addition to the SDRAM being put into self-refresh mode, the Master
Clock is set to the Slow-clock rate (32Khz) and PLLA & PLLB are
disabled.
Certain peripherals are therefore also disabled, and thus cannot be
used as wakeup sources.

This patch has been included in the AT91 patches in various forms
since 2.6.19 and a number of people have worked or commented on it,
most notably:
 Savin Zlobec (for the original AT91RM9200 support)
 Anti Sullin (for the SAM9260 version)
 David Brownell, etc.

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