hw/pci: Allow explicit function numbers in pci

hw/pci: Allow explicit function numbers in pci

Since there is no pch_gbe emulation, we could be using func other
than 0 when adding new devices to specific boards.

Signed-off-by: Chao-ying Fu <cfu@mips.com>
Signed-off-by: Djordje Todorovic <djordje.todorovic@htecgroup.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250901102850.1172983-13-djordje.todorovic@htecgroup.com>
[PMD: Compare with null character ('\0'), not '0']
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>