powerpc: fix compiling CONFIG_PPC_TRANSACTIONAL_MEM when CONFIG_ALTIVEC=n

We can't compile a kernel with CONFIG_ALTIVEC=n when
CONFIG_PPC_TRANSACTIONAL_MEM=y.  We currently get:

arch/powerpc/kernel/tm.S:320: Error: unsupported relocation against THREAD_VSCR
arch/powerpc/kernel/tm.S:323: Error: unsupported relocation against THREAD_VR0
arch/powerpc/kernel/tm.S:323: Error: unsupported relocation against THREAD_VR0
etc.

The below fixes this with a sprinkling of #ifdefs.

This was found by mpe with kisskb:
  http://kisskb.ellerman.id.au/kisskb/buildresult/8539442/

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

arch/powerpc/kernel/signal_64.c

@@ -522,10 +522,12 @@ static long restore_tm_sigcontexts(struct pt_regs *regs,
 		do_load_up_transact_fpu(&current->thread);
 		regs->msr |= (MSR_FP | current->thread.fpexc_mode);
 	}
+#ifdef CONFIG_ALTIVEC
 	if (msr & MSR_VEC) {
 		do_load_up_transact_altivec(&current->thread);
 		regs->msr |= MSR_VEC;
 	}
+#endif
 
 	return err;
 }