drm/komeda - At init write GCU control block to handle already on DPU

If something has already set up the DPU before the komeda driver comes
up, it will fail to init because it was just writing to the SRST bit in
the GCU control register and ignoring others. This resulted in TBU
bringup stalling and init failing. By writing completely we also  set the
mode back to 0 (inactive) too and thus TBU bringup works.

Signed-off-by: Carsten Haitzler <carsten.haitzler@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220606114714.175499-2-carsten.haitzler@foss.arm.com