usb: r8a66597-hcd platform data on_chip support

Convert the r8a66597-hcd driver to use the on_chip flag
from platform data to enable on chip behaviour instead
of relying on CONFIG_SUPERH_ON_CHIP_R8A66597 ugliness.

This makes the code cleaner and also allows us to support
both external and internal r8a66597 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 r8a66597 without modifying the Kconfig.

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