drm/amd/display: dont disable dtb as dto src during dpms off

drm/amd/display: dont disable dtb as dto src during dpms off

fix was previously in 25.20 but was reverted out as it was accompanied
by other changes that caused regression.

[why&how]
Disabling dtb as the dto src during dpms off relies on in the same
instance being able to also alter the dto src bit to dpref (or not dtb
in general), but this was recently changed to only take place in
dcn31_program_pix_clk, as that is where we want to perform any dto src
changes because tg is off at that point, it is unsafe to do that
elsewhere. What this means is now instead of disabling dtb as dto src
and modifying source bit, we are left with the configuration for a given
tg that specifies dtb as dto src and dtb dto en simultaneously is unset.
dcn31_program_pix_clk can rectify this but its possible for us to
perform some tg dependant  operation that would simply hang because when
we go to enable say crtc then, the clk we specify as dto src is "off" en
bit is cleared, source bit was never changed, and program_pix_clk hasnt
been called yet (as apart of dpms on)

We cant disable it as dto src during dpms off if we want the luxury of
performing tg dependant operation during dpms off and before dpms on.

Reviewed-by: Yihan Zhu <yihan.zhu@amd.com>
Signed-off-by: Ausef Yousof <Ausef.Yousof@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>