ARM: 5848/1: kill flush_ioremap_region()

There is not enough users to warrant its existence, and it is actually
an obstacle to progress with the new DMA API which cannot cover this
case properly.

To keep backward compatibility, let's perform the necessary custom
cache maintenance locally in the only driver affected.

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>