usb: musb_hcd: remove unnecessary ifdefs for dm* SoCs

The support for DaVinci DM* SoCs has been dropped. The ifdefs in the
musb_hcd driver are no longer needed. Remove them.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Marek Vasut <marex@denx.de>