arm64: mvebu: Trigger PCI devices scan at early init stage

Add PCIe initialization at early init stage.
This operation has a side effect of detecting all PCIe
plug-in cards, so the operator is not obligated to issue
"pci enum" command though CLI for this purpose.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Igal Liberman <igall@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Reviewed-by: Stefan Roese <sr@denx.de>