reverse CONFIG_ACPI_PROC_EVENT default

Sigh.  Again an ACPI assault on the Thinkpad's Fn+F4 to suspend to RAM.
The default and text for CONFIG_THINKPAD_ACPI_INPUT_ENABLED were fixed
in -rc3, but now commit 14e04fb3

 ("ACPI:
Schedule /proc/acpi/event for removal") introduces the ACPI_PROC_EVENT
config entry, and defaults it to 'n' to disable it again.

Change default to y, and add comment to make it clearer that n is for
future distros.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Len Brown <len.brown@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>