amdgpu: Wrap FPU dependent functions in dc20

dc20 containes several FPU-dependent functions without proper FPU
kernel mode enable/disable wrappers.  Add the required wrappers
for both x86 and POWER.

This enables Navi DC20 support for POWER systems.

v2: fix compilation

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>