usb: musb: Get rid of the DMA ifdefs for musb_core.c

For musb_core.c we can now just drop the DMA related
ifdef and use the already existing runtime test for
!is_cppi_enabled(musb) instead.

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