bcma: use of_dma_configure() to set initial dma mask

While fixing another bug, I noticed that bcma manually sets up
a dma_mask pointer for its child devices. We have a generic
helper for that now, which should be able to cope better with
any variations that might be needed to deal with cache coherency,
unusual DMA address offsets, iommus, or limited DMA masks, none
of which are currently handled here.

This changes the core to use the of_dma_configure(), like
we do for platform devices that are probed directly from
DT.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>