macintosh/via-pmu: Replace via pointer with via1 and via2 pointers

On most PowerPC Macs, the PMU driver uses the shift register and
IO port B from a single VIA chip.

On 68k and early PowerPC PowerBooks, the driver uses the shift register
from one VIA chip together with IO port B from another.

Replace via with via1 and via2 to accommodate this. For the
CONFIG_PPC_PMAC case, set via1 = via2 so there is no change.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>