x86/pci: Add MCFG debug logging

MCFG handling is a frequent source of problems.  Add more logging to aid in
debugging.

Enable the logging with CONFIG_DYNAMIC_DEBUG=y and the kernel boot
parameter 'dyndbg="file arch/x86/pci +p"'.

Link: https://lore.kernel.org/r/20231121183643.249006-4-helgaas@kernel.org


Tested-by: Tomasz Pala <gotar@polanet.pl>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>