platform/x86: fujitsu-laptop: merge set_lcd_level_alt() into set_lcd_level()

Depending on the value of the use_alt_lcd_levels module parameter, one
of two functions is used for setting LCD brightness level.  These
functions are almost identical and only differ in the name of the ACPI
method they call.  Instead of checking the value of use_alt_lcd_levels
at each call site, move that check to set_lcd_level() and get rid of
set_lcd_level_alt().

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