drm/msm/mdp5: fix reading hw revision on db410c platform

Since the commit commit c6122688 ("drm/msm/mdp5: stop overriding
drvdata") reading the MDP5 hw revision on db410c will crash the board
as the MDSS_GDSC is not enabled. Revert a part of the offending commit
(moving rpm enablement) and set priv->kms earlier. This make it possible
to use pm_runtime_get_sync() during read_mdp_hw_revision(), which will
power up both the MDP5 and MDSS devices.

Fixes: c6122688

 ("drm/msm/mdp5: stop overriding drvdata")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/512985/
Link: https://lore.kernel.org/r/20221125000213.252115-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>