drm/msm/dsi: Use "ref" fw clock instead of global name for VCO parent

drm/msm/dsi: Use "ref" fw clock instead of global name for VCO parent

All DSI PHY/PLL drivers were referencing their VCO parent clock by a
global name, most of which don't exist or have been renamed.  These
clock drivers seem to function fine without that except the 14nm driver
for sdm6xx [1].

At the same time all DTs provide a "ref" clock as per the requirements
of dsi-phy-common.yaml, but the clock is never used.  This patchset puts
that clock to use without relying on a global clock name, so that all
dependencies are explicitly defined in DT (the firmware) in the end.

Note that this patch intentionally breaks older firmware (DT) that
relies on the clock to be found globally instead.  The only affected
platform is msm8974 [2] for whose dsi_phy_28nm a .name="xo" fallback is
left in place to accommodate a more graceful transition period.  All
other platforms had the "ref" clock added to their phy node since its
inception, or in a followup patch some time after.  These patches
wrongly assumed that the "ref" clock was actively used and have hence
been listed as "Fixes:" below.
Furthermore apq8064 was providing the wrong 19.2MHz cxo instead of
27MHz pxo clock, which has been addressed in [3].

It is expected that both [2] and [3] are applied to the tree well in
advance of this patch such that any actual breakage is extremely
unlikely, but might still occur if kernel upgrades are performed without
the DT to match.  After some time the fallback for msm8974 can be
removed again as well.

[1]: https://lore.kernel.org/linux-arm-msm/386db1a6-a1cd-3c7d-a88e-dc83f8a1be96@somainline.org/
[2]: https://lore.kernel.org/linux-arm-msm/20210830175739.143401-1-marijn.suijten@somainline.org/
[3]: https://lore.kernel.org/linux-arm-msm/20210829203027.276143-2-marijn.suijten@somainline.org/

Fixes: d6cdf194b4ff ("arm64: dts: qcom: msm8916: Set 'xo_board' as ref clock of the DSI PHY")
Fixes: 8b18982e1291 ("ARM: dts: qcom-apq8064: Set 'cxo_board' as ref clock of the DSI PHY")
Fixes: b1a4d80c825a ("arm64: dts: sdm845: Set 'bi_tcxo' as ref clock of the DSI PHYs")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210911131922.387964-2-marijn.suijten@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>