drm/amd/display: Drop some unnecessary guards

Some of the CONFIG_DRM_AMD_DC_FP was added in some non-related FPU code,
which may cause confusion. This commit dropped some of the unnecessary
guards.

Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>