drm/amd/display: Workaround to increase phantom pipe vactive in pipesplit

[Why]
Certain high resolution displays exhibit DCC line corruption with SubVP
enabled. This is likely due to insufficient DCC meta data buffered
immediately after the mclk switch.

[How]
Add workaround to increase phantom pipe vactive height by
meta_row_height number of lines, thus increasing the amount of meta data
buffered immediately after mclk switch finishes.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>