macintosh/via-pmu: Disambiguate interrupt statistics

Some of the event counters are overloaded which makes it very
difficult to interpret their values.

Counter 0 is supposed to report CB1 interrupts but it can also count
PMU_INT_WAITING_CHARGER events.

Counter 1 is supposed to report GPIO interrupts but it can also count
other events (depending upon the value of the PMU_INT_ADB bit).

Disambiguate these statistics with dedicated counters for GPIO and
CB1 interrupts.

Comments in the MkLinux source code say that the type 0 and type 1
interrupts are model-specific. Label them as "unknown".

This change to the contents of /proc/pmu/interrupts is by necessity
visible in userland. However, packages which interact with the PMU
(that is, pbbuttonsd, pmac-utils and pmud) don't open this file.
AFAIK, user software has no need to poll these counters.

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>