usb: phy: Remove unused config

Since the old common Samsung USB PHY code has been removed by commit ea2fdf84
("usb: phy: samsung: remove old common USB PHY code"), thus remove the unused
config.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>