DM9000:Add a byte swap macro for dm9000 io operation.

commit a45dde22 changed the dm9000
direct register access to standard IO. This should work
on the ColdFire platform as there are corresponding macros for
the LE devices. But the hardware settings on some ColdFire boards had
swapped the byte order which make the original macros such as out_le16
cannot work. To avoid changing the common io access code on ColdFire
platform, the DM9000_BYTE_SWAPPED define was added to make the dm9000 use
__raw* IO access on some ColdFire boards.

Signed-off-by: Jason Jin <Jason.jin@freescale.com>