usb: host: xhci-omap: fix double weak board_usb_init functions

A weak version of the function board_usb_init is implemented in:
common/usb.c
drivers/usb/host/xhci-omap.c

To fix the double implementations:
* Convert the board_usb_init function in drivers/usb/host/xhci-omap.c
  normal (not weak).
* The function board_usb_init in drivers/usb/host/xhci-omap.c calls to
  the weak function omap_xhci_board_usb_init.
* Rename board version of the function board_usb_init to
  omap_xhci_board_usb_init.
  Done only for boards that defines CONFIG_USB_XHCI_OMAP.

To achieve the same flexibility with the function board_usb_cleanup:
* Add a normal (not weak) implementation of the function
  board_usb_cleanup in drivers/usb/host/xhci-omap.c
* The function board_usb_cleanup in drivers/usb/host/xhci-omap.c calls
  to the weak function omap_xhci_board_usb_cleanup.
* Rename board version of the function board_usb_cleanup to
  omap_xhci_board_usb_cleanup.
  Done only for boards that defines CONFIG_USB_XHCI_OMAP.

Cc: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>