drm/amdgpu: add SI DPM support (v4)

v2: corrected register offset shift
v3: rebase fixes
v4: fix firmware paths
    add SI smc firmware versions for sysfs dump
    remove unused function forward define
    fix the tahiti specific value of DEEP_SLEEP_CLK_SEL field
    fix to miss adding thermal controller
    use vram_type instead of checking mem_gddr5 flag
    fix incorrect index of CG_FFCT_0 register
    fix incorrect reading method at si_get_current_pcie_speed

Signed-off-by: Maruthi Bayyavarapu <maruthi.bayyavarapu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>