drm/amd/display: refactor dump_clk_registers

[why]
for 2 purposes:

1. get raw register value dumped on the log, which will make it easier
to talk to other team who only knows about the register

2. enable other HW to be able to use the same interface as raven to log
clock register data

Signed-off-by: Su Sung Chung <Su.Chung@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>