thinkpad-acpi: cleanup debug helpers

Fix the vdbg_printk macro definition to be sane when
CONFIG_THINKPAD_ACPI_DEBUG is undefined, and move the mess into a file
section of its own.

This doesn't change anything in the current code, but future code will
need the proper behaviour.

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