pci: imx: Add DM and DT support

Add DM support and support for probing the iMX PCI driver from DT.
The legacy non-DM support is retained, however shall be removed once
DM PCI is the only option remaining.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>