phy: fsl-imx8-mipi-dphy: Hook into runtime pm

This allows us to shut down the mipi power domain on the imx8. The
alternative would be to drop the dphy from the mipi power domain in the
SOCs device tree and only have the DSI host controller visible there but
since the PD is mostly about the PHY that would defeat it's purpose.

This allows to shut off the power domain hen blanking the LCD panel:

pm_genpd_summary before:

domain                          status          slaves
    /device                                             runtime status
----------------------------------------------------------------------
mipi                            on
    /devices/platform/soc@0/soc@0:bus@30800000/30a00300.dphy  unsupported
    /devices/platform/soc@0/soc@0:bus@30800000/30a00000.mipi_dsi  suspended

after:

mipi                            off-0
    /devices/platform/soc@0/soc@0:bus@30800000/30a00300.dphy  suspended
    /devices/platform/soc@0/soc@0:bus@30800000/30a00000.mipi_dsi  suspended

Signed-off-by: Guido Günther <agx@sigxcpu.org>
2 jobs for forward-upstream/next-20210219/dphy-runtime-pm/v4 in 204 minutes and 16 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build
passed #328625
librem5
build:aarch64:defconfig

01:24:36

 
  Package
failed #328626
librem5
pkg:aarch64:defconfig

01:59:40

 
Name Stage Failure
failed
pkg:aarch64:defconfig Package
dpkg-buildpackage: info: binary-only upload (no source included)
$ rm -f ../* || true
rm: cannot remove '../linux-imx8': Is a directory
rm: cannot remove '../linux-imx8.tmp': Is a directory
$ rm -rf "${WORKING_DIR}"; mkdir -p "${WORKING_DIR}"
$ cp -l ../*.deb ../*.changes "${WORKING_DIR}/"
cp: cannot stat '../*.deb': No such file or directory
cp: cannot stat '../*.changes': No such file or directory
ERROR: Job failed: exit code 1