ARM: bcmring: remove unused DMA map code

Remove BCMRING DMA map code which is no longer used.

This also fixes a build error with dma.c introduced by
bfcd2ea6

.

Signed-off-by: Jiandong Zheng <jdzheng@broadcom.com>
Signed-off-by: Olof Johansson <olof@lixom.net>