usb: gadget: configfs: use hexadecimal values and new line

Other unsigned properties return hexadecimal values, follow this
convention when printing b_vendor_code too. Also add newlines to
the OS Descriptor support related properties, like other sysfs
files use.

Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>