usb: musb: Add extvbus in musb_board_data

EXTVBUS programming is required by OMAP3EVM REV >=E to supply 500mA
power so adding a flag which can be used by musb driver to program
EXTVBUS.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>