ARM: vexpress: update CONFIG_USB_ISP1760 option

Commit 7ef077a8

 ("usb: isp1760: Move driver from drivers/usb/host/
to drivers/usb/isp1760/") moved the isp1760 driver and changed the
Kconfig option. This makes CONFIG_USB_ISP1760_HCD not selectable
directly anymore. This results in driver being not compiled in when
using vexpress_defconfig and the USB is non-functional.

This patch updates the CONFIG_USB_ISP1760_HCD to CONFIG_USB_ISP1760 to
get back USB functional on vexpress platforms.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reported-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>