x86/amd_nb: Simplify function 4 search

Use the newly added helper function to look up a CPU/Node function to
find "function 4" devices.

Thus, avoid the need to regularly add new PCI IDs for basic discovery.
The unique PCI IDs are still useful in case of quirks or functional
changes. And they should be used only in such a manner.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20241206161210.163701-6-yazen.ghannam@amd.com