drm/amd/display: revert to hacking bounding box for pipe split

Directly editing pipe config outside of formula is error prone
and results in higher clocks being used when splitting.
For this reason we reverted to using bounding box hacking
to split. Since sometimes this erroneusly results in higher dpm
being required we unhack the bounding box and recalculate to allow
dpm0 is possible.
Side effect is we will lose some stutter efficiency
in non dpm0 cases. This is not a big concern since increased stutter
efficiency saves an order of magnitude less power than lower dpm.

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>