drm/amd/display: Reject modes with too high pixel clock on DCE6-10

drm/amd/display: Reject modes with too high pixel clock on DCE6-10

Reject modes with a pixel clock higher than the maximum display
clock. Use 400 MHz as a fallback value when the maximum display
clock is not known. Pixel clocks that are higher than the display
clock just won't work and are not supported.

With the addition of the YUV422	fallback, DC can now accidentally
select a mode requiring higher pixel clock than actually supported
when the DP version supports the required bandwidth but the clock
is otherwise too high for the display engine. DCE 6-10 don't
support these modes but they don't have a bandwidth calculation
to reject them properly.

Fixes: db291ed1732e ("drm/amd/display: Add fallback path for YCBCR422")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>