powerpc: fix build with make 3.82

Thomas Backlund reported that the powerpc build broke with make 3.82.
It failed with the following message:

    arch/powerpc/Makefile:183: *** mixed implicit and normal rules.  Stop.

The fix is to avoid mixing non-wildcard and wildcard targets.

Reported-by: Thomas Backlund <tmb@mandriva.org>
Tested-by: Thomas Backlund <tmb@mandriva.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: stable <stable@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>