drm/amd/display: Support long vblank feature

[WHY]
We want to support low hz case, but the original
vtotal/vtotal_min/vtotal_max can't support more
than 0x7FFF.

[HOW]
We use the 2 HW reg to contorl long vblank case.
1. OTG_V_COUNT_STOP_CONTROL -> vcount_stop
2. OTG_V_COUNT_STOP_CONTROL2 -> vcount_stop_timer

vcount_stop define from which line we stop using vcount
and start using vcount2.
vcount_stop_timer define how long we use vcount2.

Ex:
Vtotal = 7
OTG_V_COUNT_STOP_CONTROL = 4
OTG_V_COUNT_STOP_CONTROL2 = 5

time    : 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
vcount  : 0, 1, 2, 3, -  -  -  -  -  4,  5,  6
vcount2 :             0, 1, 2, 3, 4,

Reviewed-by: Jun Lei <jun.lei@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: ChunTao Tso <chuntao.tso@amd.com>
Signed-off-by: Robin <Chen&lt;robin.chen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>