imx: ventana: various board-specific GPIO config updates

- Added iomux for CAN_STBY and RS484_TEN (GW52xx/GW53xx/GW54xx/GW551x)
- Moved iomux of USBHUB_RST# out of board_ehci_hcd_init so that it is
  done regardless of USB being initialized in bootloader
- Added usb_sel iomux/hwconfig for GW552x
- Fixed mezzanine DIO for GW54xx
- Fixed PANLEDR# for GW54xx
- Fixed dio iomux/hwconfig for GW552x
- Fixed dio iomux for GW551x
- removed redundant #define

Signed-off-by: Tim Harvey <tharvey@gateworks.com>