drm/amd/pm: update smartshift powerboost calc for smu13

smartshift apu and dgpu power boost are reported as percentage
with respect to their power limits. adjust the units of power before
calculating the percentage of boost.

Signed-off-by: Sathishkumar S <sathishkumar.sundararaju@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>