dp8393x: Clean up endianness hacks

dp8393x: Clean up endianness hacks

According to the datasheet, section 3.4.4, "in 32-bit mode ... the SONIC
always writes long words".

Therefore, use the same technique for the 'in_use' field that is used
everywhere else, and write the full long word.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 46ffee9ad43185cbee4182c208bbd534814086ca)
 Conflicts:
	hw/net/dp8393x.c
*roll in local dependencies on b7cbebf2b9d
*drop functional dep. on 19f70347731
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>