ACPI: ibm-acpi: rename driver to thinkpad-acpi

Rename the ibm-acpi driver to thinkpad-acpi.  ThinkPads are not even made
by IBM anymore, so it is high time to rename the driver...

The name thinkpad-acpi was used sometime ago by a thinkpad-specific hotkey
driver by Erik Rigtorp, around the 2.6.8-2.6.10 time frame.  The driver
apparently never got merged into mainline (it did make some trips through
-mm).  ibm-acpi was merged soon after, making its debut in 2.6.10.

The reuse of the thinkpad-acpi name shouldn't be a problem as far as user
confusion goes, as Erik's thinkpad-acpi apparently didn't get widespread
use in the Linux ThinkPad community and most hits for thinkpad-acpi in
google point to ibm-acpi anyway.

Erik, if you read this, please consider the reuse of the thinkpad-acpi name
as a compliment to your effort to make ThinkPads more useful to all of us.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>