x86/PCI: Preserve existing pci=bfsort whitelist for Dell systems

Commit 6e8af08d enables pci=bfsort on
future Dell systems. But the identification string 'Dell System' matches
on already existing whitelist, which do not have SMBIOS type 0xB1,
causing pci=bfsort not being set on existing whitelist.

This patch fixes the regression by moving the type 0xB1 check beyond the
existing whitelist so that existing whitelist is walked before.

Signed-off-by: Shyam Iyer <shyam_iyer@dell.com>
Signed-off-by: Narendra K <narendra_k@dell.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>