PCI: ls-gen4: Rename ls_pcie_g4 to ls_g4_pcie

Rename struct ls_pcie_g4 to ls_g4_pcie to match the convention of
<driver>_pcie. No functional change intended.

Link: https://lore.kernel.org/r/20211223011054.1227810-14-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>