pci: fsl: Change compatible string for mpc8548 to "fsl, mpc8548-pcie"

Upstream Linux kernel uses for mpc8548-based PCIe controllers compatible
string "fsl,mpc8548-pcie". So change U-Boot fsl PCIe driver and all DTS
files to use "fsl,mpc8548-pcie" instead of "fsl,pcie-mpc8548" to be
compatible with Linux kernel.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>