drm/amd/display: Modified set bandwidth sequence.

This change make sure bandwidth is set properly.
For increase bandwidth, set bandwidth before backend
and front end programming.
For decrease bandwidth, set bandwidth after.
To avoid smu hang when reboot and dpms due to 0 disp clk,
keep min disp clock as 100Mhz.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>