PCI: rcar-gen4: Replace of_device.h with explicit of.h include

The DT of_device.h and of_platform.h date back to the separate
of_platform_bus_type before it was merged into the regular platform
bus.

As part of that merge prepping Arm DT support 13 years ago, they
"temporarily" include each other. They also include platform_device.h
and of.h.

As a result, there's a pretty much random mix of those include files
used throughout the tree. In order to detangle these headers and replace
the implicit includes with struct declarations, users need to explicitly
include the correct includes.

[kwilczynski: commit log]
Link: https://lore.kernel.org/linux-pci/20231207165251.2855783-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>