imx: usb: ehci-mx6: document board specific functions

Document target board specific functions

board_ehci_hcd_init - override usb phy mode
board_ehci_hcd_init - set usb vbus voltage
board_ehci_power - enables/disables usb vbus voltage

Signed-off-by: Adrian Alonso <aalonso@freescale.com>
1 file changed