ARM: OMAP2+: SmartReflex: add POWER_AVS Kconfig options

Add a Kconfig menu (POWER_AVS) and rename the Kconfig options
for the OMAP SmartReflex implementation:
	CONFIG_OMAP_SMARTREFLEX renames to CONFIG_POWER_AVS_OMAP
	CONFIG_OMAP_SMARTREFLEX_CLASS3 renames to CONFIG_POWER_AVS_OMAP_CLASS3

This change makes the SmartReflex implementation ready for the move
to drivers/.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: J Keerthy <j-keerthy@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>