platform/x86: fujitsu-laptop: clean up use_alt_lcd_levels handling

The value of each module parameter can be changed on the fly via sysfs.
However, the current way of handling use_alt_lcd_levels prevents the
user from dynamically switching from a value of 0 or 1 back to
autodetection as the latter is only performed upon ACPI device
instantiation.  Fix this by moving autodetection (in a simplified form)
to set_lcd_level() and changing module parameter type to int.  Do not
announce autodetection results in a debug message as current value of
use_alt_lcd_levels can simply be read from sysfs.  Clarify module
parameter description.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>