mach-snapdragon: implement ft_board_setup() for USB role selection

Some Qualcomm boards have only one USB controller which is muxed between
the type-c port and an internal USB hub for type-A and ethernet. We
modify the DT for these to force them to host mode in U-Boot. However in
Linux DRD role switching is supported (required, even). Use
ft_board_setup() to adjust the dr_mode property for these boards.

While we're here, define pr_fmt for this file so we can more easily
identify log messages.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>