drm/amd/display: Adjust DCE 8-10 clock, don't overclock by 15%

Adjust the nominal (and performance) clocks for DCE 8-10,
and set them to 625 MHz, which is the value used by the legacy
display code in amdgpu_atombios_get_clock_info.

This was tested with Hawaii, Tonga and Fiji.
These GPUs can output 4K 60Hz (10-bit depth) at 625 MHz.

The extra 15% clock was added as a workaround for a Polaris issue
which uses DCE 11, and should not have been used on DCE 8-10 which
are already hardcoded to the highest possible display clock.
Unfortunately, the extra 15% was mistakenly copied and kept
even on code paths which don't affect Polaris.

This commit fixes that and also	adds a check to	make sure
not to exceed the maximum DCE 8-10 display clock.

Fixes: 8cd61c31 ("drm/amd/display: Raise dispclk value for Polaris")
Fixes: dc88b4a6 ("drm/amd/display: make clk mgr soc specific")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Rodrigo Siqueira <siqueira@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>