usb: musb: Kconfig: Select the DMA driver if DMA mode of MUSB is enabled

AM335x MUSB supports both PIO and DMA mode. When DMA mode is
selected users need to explicitly enable the DMA driver. To avoid the
extra configuration select the DMA driver if DMA mode is set for AM335x MUSB.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>