drm/amd/display: Decrease stack size in logging path

[why]
Reducing stack size can avoid stack over flow

[how]
Make local variables const and static so they are not
on the stack.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Reza Amini <reza.amini@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>