drm/amd/display: Fix DCE 6.0 and 6.4 PLL programming.

Apparently, both DCE 6.0 and 6.4 have 3 PLLs, but PLL0 can only
be used for DP. Make sure to initialize the correct amount of PLLs
in DC for these DCE versions and use PLL0 only for DP.

Also, on DCE 6.0 and 6.4, the PLL0 needs to be powered on at
initialization as opposed to DCE 6.1 and 7.x which use a different
clock source for DFS.

The following functions were used as reference from the	old
radeon driver implementation of	DCE 6.x:
- radeon_atom_pick_pll
- atombios_crtc_set_disp_eng_pll

Reviewed-by: Rodrigo Siqueira <siqueira@igalia.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 35222b59)
Cc: stable@vger.kernel.org