thinkpad-acpi: fix LED blinking through timer trigger

The set_blink hook code in the LED subdriver would never manage to get
a LED to blink, and instead it would just turn it on.  The consequence
of this is that the "timer" trigger would not cause the LED to blink
if given default parameters.

This problem exists since 2.6.26-rc1.

To fix it, switch the deferred LED work handling to use the
thinkpad-acpi-specific LED status (off/on/blink) directly.

This also makes the code easier to read, and to extend later.

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