ARM: dma-mapping: Remove traces of NOMMU code

DMA operations for NOMMU case have been just factored out into
separate compilation unit, so don't keep dead code.

Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Tested-by: Andras Szemzo <sza@esh.hu>
Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>