usb: renesas_usbhs: add SoC names to compatibility string documentation

This extends the documentation of compatibility strings a little to
include the SoC names.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>