drm/msm/dpu: Issue MDSS reset during initialization

drm/msm/dpu: Issue MDSS reset during initialization

It's typical for the bootloader to bring up the display for showing a
boot splash or efi framebuffer. But in some cases the kernel driver ends
up only partially configuring (in particular) the DPU, which might
result in e.g. that two different data paths attempts to push data to
the interface - with resulting graphical artifacts.

Naturally the end goal would be to inherit the bootloader's
configuration and provide the user with a glitch free handover from the
boot configuration to a running DPU.

But as implementing seamless transition from the bootloader
configuration to the running OS will be a considerable effort, start by
simply resetting the entire MDSS to its power-on state, to avoid the
partial configuration.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/482796/
Link: https://lore.kernel.org/r/20220421041550.643964-2-bjorn.andersson@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>