drm/amd/display: Set i2c memory to light sleep during hw init

[WHY]
i2c memory doesn't get set to light sleep on hw init as intended

[HOW]
Set i2c to light sleep after reg gets zeroed, ensuring memory power
control doesn't get disabled for any other DIO memory

Reviewed-by: Haonan Wang <Haonan.Wang2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Acked-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>