drm/amd/display/dml2: Guard dml21_map_dc_state_into_dml_display_cfg with DC_FP_START

drm/amd/display/dml2: Guard dml21_map_dc_state_into_dml_display_cfg with DC_FP_START

dml21_map_dc_state_into_dml_display_cfg calls (the call is usually
inlined by the compiler) populate_dml21_surface_config_from_plane_state
and populate_dml21_plane_config_from_plane_state which may use FPU.  In
a x86-64 build:

    $ objdump --disassemble=dml21_map_dc_state_into_dml_display_cfg \
    > drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_translation_helper.o |
    > grep %xmm -c
    63

Thus it needs to be guarded with DC_FP_START.  But we must note that the
current code quality of the in-kernel FPU use in AMD dml2 is very much
problematic: we are actually calling DC_FP_START in dml21_wrapper.c
here, and this translation unit is built with CC_FLAGS_FPU.  Strictly
speaking this does not make any sense: with CC_FLAGS_FPU the compiler is
allowed to generate FPU uses anywhere in the translated code, perhaps
out of the DC_FP_START guard.  This problematic pattern also occurs in
at least dml2_wrapper.c, dcn35_fpu.c, and dcn351_fpu.c.  Thus we really
need a careful audit and refactor for the in-kernel FPU uses, and this
patch is simply whacking a mole.  However per the reporter, whacking
this mole is enough to make a 9060XT "just work."

Reported-by: Asiacn <710187964@qq.com>
Closes: https://github.com/loongson-community/discussions/issues/102
Tested-by: Asiacn <710187964@qq.com>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>