drm/amdgpu/smu_v11: Unify and fix power limits

[Why]
On Navi10, and presumably arcterus, updating pp_table via sysfs would
not re-scale the maximum possible power limit one can set. On navi10,
the SMU code ignored the power percentage overdrive setting entirely,
and would not allow you to exceed the default power limit at all.

[How]
Adding a function to the SMU interface to get the pptable version of the
default power limit allows ASIC-specific code to provide the correct
maximum-settable power limit for the current pptable.

v3: fix spelling (Alex)

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Matt Coffin <mcoffin13@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>