drm/amd/display: Share dce100_validate_bandwidth with DCE6-8

drm/amd/display: Share dce100_validate_bandwidth with DCE6-8

DCE6-8 have very similar capabilities to DCE10, they support the
same DP and HDMI versions and work similarly.

Share dce100_validate_bandwidth between DCE6-10 to reduce code
duplication in the DC driver.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>