PCI: mediatek-gen3: Rename mtk_pcie_port to mtk_gen3_pcie

Rename struct mtk_pcie_port to mtk_gen3_pcie to match the convention of
<driver>_pcie. No functional change intended.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Fan Fei <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Cc: Ryder Lee <[email protected]>
Cc: Jianjun Wang <[email protected]>

Author: firebolt007