phy-rcar-usb: remove EHCI internal buffer setup

Now that the EHCI internal  buffer setup is done by the platform code,  we  can
remove  such code from this driver as it  never  really belonged here.  We also
no longer need the 2nd memory region now (2nd EHCI controller is simply missing
in e.g. R8A7778 SoC).

The patch has been tested on the Marzen and BOCK-W boards.

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