drm/amd/display: Remove FPU guards from the DML folder

As part of the programming expectation for using DML functions, DC
requires that any DML function invoked outside DML uses:

 DC_FP_START();
 ... dml function ...
 DC_FP_END();

Additionally, all the DML functions that can be invoked outside the DML
folder call the function dc_assert_fp_enabled(), which is responsible
for triggering a warning in the case that the DML function was not
guarded by the DC_FP_START/END. For this reason, call DC_FP_START/END
inside DML is wrong, and this commit removes all of those references.

Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>