make /proc/acpi/ac_adapter dependent on ACPI_PROCFS

Do not provide /proc/acpi/ac_adapter if ACPI_PROCFS is not defined.  This
eliminates duplicated power adapters in HAL and makes it consistent with
battery module

Signed-off-by: Andrey Borzenkov <arvidjaar@mail.ru>
Acked-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>