OMAP3: PM: Added support for L2 aux ctrl register save and restore

This patch adds a save and restore mechanism for ARM L2 auxiliary control
register. The feature is enabled by default for GP devices, but for HS/EMU
devices the user must enable the service and define the PPA service ID to
be used for setting L2 aux ctrl, as this is not currently supported by the
bootloader. If nobody alters the contents of L2 aux ctrl from its reset
value, this feature is not needed.

Kconfig option to enable HS/EMU L2 aux save and restore:
- OMAP3_L2_AUX_SECURE_SAVE_RESTORE
Kconfig option to select HS/EMU PPA service for setting L2 aux ctrl:
- OMAP3_L2_AUX_SECURE_SERVICE_SET_ID

Signed-off-by: Tero Kristo <tero.kristo@nokia.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>