ACPI: thinkpad-acpi: use bitfields for module flags

Use a bitfield to hold boolean module-wide flags, to conserve some memory.
It is easy and it is clean, so we do it just for the heck of it even if it
saves very little space.

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