powerpc/83xx: Add power management support for MPC837x boards

powerpc/83xx: Add power management support for MPC837x boards

This patch adds pmc nodes to the device tree files so that the boards
will able to use standby capability of MPC837x processors. The MPC837x
PMC controllers are compatible with MPC8349 ones (i.e. no deep sleep).

sleep = <> properties are used to specify SCCR masks as described
in "Specifying Device Power Management Information (sleep property)"
chapter in Documentation/powerpc/booting-without-of.txt.

Since I2C1 and eSDHC controllers share the same clock source, they
are now placed under sleep-nexus nodes.

A processor is able to wakeup the boards on LAN events (Wake-On-Lan),
console events (with no_console_suspend kernel command line), GPIO
events and external IRQs (IRQ1 and IRQ2).

The processor can also wakeup the boards by the fourth general purpose
timer in GTM1 block, but the GTM wakeup support isn't yet implemented
(it's tested to work, but it's unclear how can we use the quite short
GTM timers, and how do we want to expose the GTM to userspace).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>