ACPI: thinkpad-acpi: allow use of CMOS NVRAM for brightness control
It appears that Lenovo, in its efforts to support Vista's ACPI 2.0, decided
to break the EC brightness control interface in a weird way. Fortunately,
the old CMOS NVRAM interface works just fine in the Lenovo ThinkPad models.
Add a module parameter that allows the user to select which strategy to use
for brightness control: EC, NVRAM, or both. By default, do both (which is
the way thinkpad-acpi used to work until now) on IBM ThinkPads, and use
NVRAM only on Lenovo ThinkPads.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>