fujitsu-laptop: Simplify SBLL/SBL2 backlight handling

GBLS and GBLL only differ in the clearing of the GHKS flag, so there is no need
to have two backlight level readouts. Also, per Peter Gruber, the need for the
BLNF check has disappeared.
As a result, cleanups can be made in the code. This has been tested on the both
the S6410 and the S6420 platforms and causes no functionality regressions, on
the console without X or within X. One module parameter to disable the hotkeys
is dropped, as we only ever took one codepath anyway.

Signed-off-by: Tony Vroon <tony@linx.net>
Tested-by: Peter Gruber <nokos@gmx.net>
Tested-By: Stephen Gildea <stepheng+linux@gildea.com>
Acked-by: Jonathan Woithe <jwoithe@physics.adelaide.edu.au>
Signed-off-by: Len Brown <len.brown@intel.com>