powerpc: Simplify push_end definition in pci_32.c

The push_end macro in arch/powerpc/kernel/pci_32.c uses integer
division and multiplication to achieve the effect of rounding a
resource end address up and then advancing it to the end of a
power-of-2 sized region.  This changes it to an equivalent computation
that only needs an integer add and OR.  This is partly based on an
earlier patch by Mel Gorman.

Signed-off-by: Paul Mackerras <paulus@samba.org>