drm/amd/display: Add interface to adjust DSC max target bpp limit

[Why]
For some use cases we need to be able to adjust the maximum target bpp
allowed by DSC policy.

[How]
New interface dc_dsc_policy_set_max_target_bpp_limit

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Nikola Cornij <Nikola.Cornij@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>