drm/amd/display: Change i2c speed for hdcp

[why]
HDCP 1.4 failed on SL8800 SW w/a test driver use.

[how]
slower down the HW i2c speed when used by HW i2c.

Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Reviewed-by: Aurabindo Pillai <Aurabindo.Pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>