usb: musb: Allow building in all the DMA code

With recent changes to MUSB code, we can now now get rid of
the Kconfig choise for the DMA code and allow building in any
of the desired DMA code. This makes life easier for distros.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>