usb: musb: remove a few is_dma_capable() in init/exit code

This patch removes is_dma_capable() and an ifdef in the init/exit path
around init/de-init of the dma_controller. Since we have the empty stubs
in the PIO code we can call it without gcc trouble. Earlier we had an
ifdef and the is_dma_capable() macro where gcc ignored the if (0) path
even that the function was not around :)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>