drm/amd/display: add guard for SMU ver, for 48mhz clk

[why]
dp_48m_refclk_driver_pwdn is persistent through S3 and S5.
This was worked arround in SMU FW 55.21.0. Earlier FW don't have this fix
so we will hang on reboot

[how]
add a guard for smu versions before SMU FW 55.21.0

Signed-off-by: Joseph Gravenor <joseph.gravenor@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>