firmware: dmi_scan: Save SMBIOS Type 9 System Slots

Save SMBIOS Type 9 System Slots during DMI scan. PCI address of
onboard devices was already saved but not for slots.

Signed-off-by: Jordan Hargrave <jordan_hargrave@dell.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>