drm/amd/display: Reduce default backlight min from 5 nits to 1 nits

[Why & How]
Currently set_default_brightness_aux function uses 5 nits as lower limit
to check for valid default_backlight setting. However some newer panels
can support even lower default settings

Reviewed-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Swapnil Patel <swapnil.patel@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>