msm: mdss: set pipe to solid fill when releasing it

There are cases where pipe can remain active for additional vsync after
unstaging from mixer, if this ever happens it will keep fetching from
memory. In order to avoid this, we can setup the pipe in solid fill mode
so there is no memory access after pipe is released by software and
avoid potential iommu page fault or underrun since pipe is no longer
considered for bandwidth calculations.

Change-Id: I4b5a5deda8c854c504ef523df434509fa5567186
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>