sparc64: cleanup after SunOS/Solaris binary emulation removal

The following cleanups are now possible:
- arch/sparc64/kernel/entry.S:ret_sys_call no longer has to be global
- arch/sparc64/kernel/sparc64_ksyms.c:
  remove no longer used prototypes

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>