OMAP PM: remove OMAP_PM_NONE config option

The current code base is not linking with the OMAP_PM_NONE
option set.
Since the option OMAP_PM_NOOP provides a no-op/debug layer,
OMAP_PM_NONE can be removed.
OMAP_PM_NOOP is enabled by default by Kconfig.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>