drm/amdgpu/display: Enable DC_FP for LoongArch

LoongArch now provides kernel_fpu_begin() and kernel_fpu_end() that are
used like the x86 counterparts in commit 2b3bd32e ("LoongArch:
Provide kernel fpu functions"), so we can enable DC_FP on LoongArch for
supporting more DCN devices.

Signed-off-by: WANG Xuerui <kernel@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>