Add arch-specific ioremap() which uses any existing static mappings
in place of doing a new mapping.  From now on, drivers should always
use ioremap() instead of IO_ADDRESS().

In addition, remove the davinci_[read|write]* macros in favor of using
ioremap + io[read|write]*.
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>