MIPS: malta: add support for PCI driver model

MIPS: malta: add support for PCI driver model

As almost all peripherals are connected via PCI dependent on the
used core card, PCI setup is always required. Thus run pci_init()
including PCI scanning and probing and core card specific setups
in board_early_init_r().

Also prepare support for dynamically managing the status of the
different PCI DT nodes dependent on used core card via option
CONFIG_OF_BOARD_FIXUP. Before this feature can be enabled,
the call order of the fix_fdt() init hook in board_init_f
needs to be changed. Otherwise rw_fdt_blob points to a read-only
NOR flash address. Thus this options needs to stay disabled
until the board_init_f problem could be solved. This breaks
running the default U-Boot image on real HW using the FPGA core
card but Qemu emulation still works. Currently Qemu is more
important as MIPS CI tests depend on Malta and the deadline
for PCI DM conversion will be enforced soon.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>