acpi: make ACPI_PROCFS default to y

Zillions of people are getting my-battery-monitor-doesnt-work problems
(including me).

Lessen the damage by making ACPI_PROCFS default to on.

Cc: Len Brown <lenb@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>