[pci][dw][aml] Refactor AMLogic PCIe Driver

Refactor the AMLogic PCIe driver into two halves:

(1) The DesignWare PCIe Library
(2) The AMLogic PCIe Driver

The AMLogic Driver statically links against the DesignWare PCIe
Library. Logic that is common to the DesignWare IP exists only in
the library whereas individual SoCs can implement their own drivers
that use the common DesignWare code.

Subsequent CLs will introduce the HiSilicon implementation of the DW
PCIe block as well.

TEST: Booted on gauss and confirmed that PCI bus driver started,
published devices and that devices were able to bind.

Change-Id: I76a438c5781e649d3f274de20378bd6d29e21868