drm/amd/display: Add two dmmuy I2C entry for GPIO port mapping issue

[Why]
When only 4 I2C is declared, two dummies are required to correctly map
GPIO port.

[How]
Add one more I2C dummy entry to match GPIO port.

Signed-off-by: Chris Park <chris.park@amd.com>
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>