selftests/powerpc: Add missing binaries to .gitignores

Some of the recent new selftests were missing additions to .gitignore,
add them now.

Signed-off-by: Michael Ellerman <[e-mail]>

tools/testing/selftests/powerpc/math/.gitignore

···
 vmx_preempt
 fpu_signal
 vmx_signal
+vsx_preempt

tools/testing/selftests/powerpc/signal/.gitignore

···
+signal
+signal_tm

tools/testing/selftests/powerpc/tm/.gitignore

···
 tm-tar
 tm-tmspr
 tm-exec
+tm-signal-context-chk-fpu
+tm-signal-context-chk-gpr
+tm-signal-context-chk-vmx
+tm-signal-context-chk-vsx