usb: m66592-udc platform data on_chip support

Convert the m66592-udc driver to use the on_chip flag
from platform data to enable on chip behaviour instead
of relying on CONFIG_SUPERH_BUILT_IN_M66592 ugliness.

This makes the code cleaner and also allows us to support
both external and internal m66592 with the same kernel.

It also makes the Kconfig part more future proof since
we with this patch can add support for new processors
with on-chip m66592 without modifying the Kconfig.

The patch adds a m66592 header file for platform data
and ties in platform data to the existing m66592 devices.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>