PCI: imx6: Call host init function directly in resume

Call imx6_pcie_host_init() instead of duplicating codes in resume.  Note
that this also means we do MPLL setup again during resume, which we didn't
do before.

[bhelgaas: add MPLL setup note, pointed out by Lucas]
Link: https://lore.kernel.org/r/1657783869-19194-10-git-send-email-hongxing.zhu@nxp.com
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>