misc: microchip: pci1xxxx: load auxiliary bus driver for the PIO function in the multi-function endpoint of pci1xxxx device.

pci1xxxx is a PCIe switch with a multi-function endpoint on one of its
downstream ports. PIO function is one of the functions in the
multi-function endpoint. PIO function combines a GPIO controller and also
an interface to program pci1xxxx's OTP & EEPROM. This auxiliary bus driver
is loaded for the PIO function and separate child devices are enumerated
for GPIO controller and OTP/EEPROM interface.

Signed-off-by: Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>
Link: https://lore.kernel.org/r/20220824200047.150308-2-kumaravel.thiagarajan@microchip.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>