powerpc/85xx: Replace CONFIG_USB_ISP1760_HCD by CONFIG_USB_ISP1760

Since commit 100832ab

 ("usb: isp1760: Make HCD support
optional"), CONFIG_USB_ISP1760_HCD is automatically selected when
needed.  Enabling that option in the defconfig is now a no-op, and no
longer enables ISP1760 HCD support.

Re-enable the ISP1760 driver in the defconfig by enabling
USB_ISP1760_HOST_ROLE instead.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Scott Wood <scottwood@freescale.com>