drm/amd/display: add explicit handshake between x86 and DMCU

[why]
When DMCU interrupts x86, it leads to undefined phy programming

[how]
expand dmcu interface to support new PHY lock and unlock commands
if DMCU FW doesn't support these commands, they fail silently so its okay

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>