ARM: omap2: Get USB hub reset GPIO from descriptor

This switches the USB hub GPIO reset line handling in the
OMAP2 pdata quirks over to using GPIO descriptors to avoid using
the global GPIO numberspace.

Since the GPIOs are exported and assumedly used by some kind
of userspace we cannot simply use hogs in the device tree.

Fixes: 92bf78b3 ("gpio: omap: use dynamic allocation of base")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>