drm/amd/display: Increase sr enter/exit in rn ddr4 watermark table

[Why]
After removing added latency for HostVM by default, DDR4 sr exit
latencies were no longer large enough for some panels and caused
underflow.

[How]
Add 1us to sr enter/exit watermark.

Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>