PCI: mobiveil: Improve PCIE_LAYERSCAPE_GEN4 dependencies

PCI: mobiveil: Improve PCIE_LAYERSCAPE_GEN4 dependencies

  - Drop the dependency on PCI, as this is implied by the dependency on
    PCI_MSI_IRQ_DOMAIN,
  - Drop the dependencies on OF and ARM64, as the driver compiles fine
    without OF and/or on other architectures,
  - The Freescale Layerscape PCIe Gen4 controller is present only on
    Freescale Layerscape SoCs.  Hence depend on ARCH_LAYERSCAPE, to
    prevent asking the user about this driver when configuring a kernel
    without Freescale Layerscape support, unless compile-testing.

Link: https://lore.kernel.org/r/20210208142301.413582-1-geert+renesas@glider.be
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>