usb: musb: Add 'extvbus' in musb_hdrc_platform_data

Some of the board might use external Vbus power supply on musb
interface which would require to program ULPI_BUSCONTROL register.

Adding 'extvbus' flag which can be set from such boards which will
be checked at musb driver files before programming ULPI_BUSCONTROL.

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>