usb: allow sh7724 to enable on-chip r8a66597

The sh7724 processor has two on-chip r8a66597 blocks, so add
it to the list of processors for SUPERH_ON_CHIP_R8A66597.

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