dell-laptop: extract SMBIOS-related code to a separate module

Extract SMBIOS-related code from dell-laptop to a new kernel module,
dell-smbios.  The static specifier is removed from exported symbols,
otherwise code is just moved around.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
[dvhart: Include linux/io.h in dell-smbios.c as caught by lkp]
Signed-off-by: Darren Hart <dvhart@linux.intel.com>