platform/x86: fujitsu-laptop: replace numeric values with constants

Replace three repeating numeric values with constants to improve code
clarity.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
[kempniu: rebase patch, rewrite commit message]
Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>