drm/amd/display: eliminate long wait between register polls on Maximus

[Why]
Now that we "scale" time delays correctly on Maximus (as of diags svn
r170115), the forced "35 ms" wait time now becomes 35 ms * 500 = 17.5
seconds, which is far too long.  Even having to repeat polling a
register once causes excessive delays on Maximus.

[How]
Just use the regular wait time passed to the generic_reg_wait()
function.  This is sufficient for Maximus now, and it also means that
there's one less "Maximus-only" code path in DAL.

Also disable the "REG_WAIT taking a while:" message on Maximus, since
things do take a while longer there and 1-2ms delays are not uncommon
(and nothing to worry about).

Signed-off-by: Ken Chalmers <ken.chalmers@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>