sparc32: replace flip_dword() with swab32()

The latter is a generic implmentation.
flip_{,d}word() is sparc32 specific and will be dropped.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Hellstrom <daniel@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>