drm/amd/display: Reuse parsing code of debugfs write buffer

[why]
Move code for parsing debugfs input into an array of int parameters by
specifying the max number of expected parameters

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>