thinkpad-acpi: don't ask about brightness_mode for fw. 1V and 1R

X40 (firmware 1V) and T41 (firmware 1R) have been confirmed to work
well with the new defaults, so we can stop pestering people to confirm
that fact.

For now, whitelist just these two firmware types.  It is best to have
at least one more firmware type confirmed for Radeon 9xxx and Intel
GMA-2 ThinkPads before removing the confirmation requests entirely.

Reported-by: Robert de Rooy <robert.de.rooy@gmail.com>
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: stable@kernel.org
Signed-off-by: Len Brown <len.brown@intel.com>