sparc: combine unistd_{32,64}.h

This is complicated a little because compat_audit.c wants to see only
the 32bit syscall numbers, but is being built in a 64bit compile.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>