powerpc: Use standard macros for sys_sigpending() & sys_old_getrlimit()

Currently we have sys_sigpending and sys_old_getrlimit defined to use
COMPAT_SYS() in systbl.h, but then both are #defined to sys_ni_syscall
in systbl.S.

This seems to have been done when ppc and ppc64 were merged, in commit
9994a338 "Introduce entry_{32,64}.S, misc_{32,64}.S, systbl.S".

AFAICS there's no longer (or never was) any need for this, we can just
use SYSX() for both and remove the #defines to sys_ni_syscall.

The expansion before was:

  #define COMPAT_SYS(func)	.llong	.sys_##func,.compat_sys_##func
  #define sys_old_getrlimit sys_ni_syscall
  COMPAT_SYS(old_getrlimit)
  =>
  .llong	.sys_old_getrlimit,.compat_sys_old_getrlimit
  =>
  .llong	.sys_ni_syscall,.compat_sys_old_getrlimit

After is:

  #define SYSX(f, f3264, f32)	.llong	.f,.f3264
  SYSX(sys_ni_syscall, compat_sys_old_getrlimit, sys_old_getrlimit)
  =>
  .llong	.sys_ni_syscall,.compat_sys_old_getrlimit

ie. they are equivalent.

Finally both COMPAT_SYS() and SYSX() evaluate to sys_ni_syscall in the
Cell SPU code.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>