Introduce DC_FP_START()/DC_FP_END() macros to help enable floating
point kernel mode support across various architectures.

v2: move copyright update to commit which adds the changes
Signed-off-by: NTimothy Pearson <tpearson@raptorengineering.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>