When we want to use float point operation on Linux
we need to use within special kernel protection
(`kernel_fpu_{begin,end}()`.), otherwise the kernel
can clobber userspace FPU register state. For detecting
these issues we use a tool named objtool (with -Ffa
flags) to highlight the FPU problems, all warnings can
be summed up as follows:

./tools/objtool/objtool check -Ffa
drivers/gpu/drm/amd/display/dc/dml/dml_common_defs.o

[..] dc/dsc/rc_calc.o: warning: objtool: get_qp_set()+0x2f8:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc.o: warning: objtool: dsc_roundf()+0x5:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc.o: warning: objtool: dsc_ceil()+0x5:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc.o: warning: objtool: get_ofs_set()+0x3eb:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc.o: warning: objtool: calc_rc_params()+0x3c:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/dc_dsc.o: warning: objtool:
get_dsc_bandwidth_range.isra.0()+0x8d:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/dc_dsc.o: warning: objtool: setup_dsc_config()+0x2ef:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc_dpi.o: warning: objtool:copy_pps_fields()+0xbb:
FPU instruction outside of kernel_fpu_{begin,end}()
[..] dc/dsc/rc_calc_dpi.o: warning: objtool:
dscc_compute_dsc_parameters()+0x7b:
FPU instruction outside of kernel_fpu_{begin,end}()

This commit fixes the above issues by rework DSC as described:

1. Isolate all FPU operations in a single file;
2. Use FPU flags only in the file that handles FPU operations;
3. Isolate all functions that require float point operation in static
   functions;
4. Add a mid-layer function that does not use any float point operation,
   and that could be safely invoked in other parts of the code.
5. Keep float point operation under DC_FP_{START/END} macro.

CC: Christian König <christian.koenig@amd.com>
CC: Alexander Deucher <Alexander.Deucher@amd.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Tony Cheng <tony.cheng@amd.com>
CC: Harry Wentland <hwentlan@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Mikita Lipski <Mikita.Lipski@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>