drm/amd/display: Only force modesets when toggling HDR

[Why]
We can issue HDR static metadata as part of stream updates for
non-modesets as long as we force a modeset when entering or exiting HDR.

This avoids unnecessary blanking for simple metadata updates.

[How]
When changing scaling and abm for the stream also check if HDR has
changed and send the stream update. This will only happen in non-modeset
cases.

Cc: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528190836.10738-3-nicholas.kazlauskas@amd.com