sparc: unify stat.h

To my suprise struct stat64 was not equal on sparc 32 and sparc64,
so there was really nothing to share here.
Unify the files by adding their respective content to stat.h.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>