usb: kconfig: remove dependency FSL_SOC for ehci fsl driver

CONFIG_USB_EHCI_FSL is not dependent on FSL_SOC, it can be built on
non-PPC platforms.

Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>
Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>