soft-fp: Add implementation for 128 bit self-contained

soft-fp: Add implementation for 128 bit self-contained

Here only add the implementation when building the RV32 port.

These macros are used when the following situations occur at the same
time: soft-fp fma, ldbl-128 and 32-bit _FP_W_TYPE_SIZE. The RISC-V
32-bit port is the first port which use all three together.

This is the building flow about the situation:
When building soft-fp/s_fmal.c, there uses the FP_FMA_Q in __fmal.
The _FP_W_TYPE_SIZE is defined to 32-bit in sysdeps/riscv/sfp-machine.h,
so the FP_FMA_Q was defined to _FP_FMA (Q, 4, 8, R, X, Y, Z) in
soft-fp/quad.h.

Something in the soft-fp/quad.h:
 #if _FP_W_TYPE_SIZE < 64
    # define FP_FMA_Q(R, X, Y, Z)    _FP_FMA (Q, 4, 8, R, X, Y, Z)
 #else
    # define FP_FMA_Q(R, X, Y, Z)    _FP_FMA (Q, 2, 4, R, X, Y, Z)
 #endif

Finally, in _FP_FMA (fs, wc, dwc, R, X, Y, Z), it will use the
_FP_FRAC_HIGHBIT_DW_##dwc macro, and it will be expanded to
_FP_FRAC_HIGHBIT_DW_8, but the _FP_FRAC_HIGHBIT_DW_8 is not be
implemented in soft-fp/op-8.h. there is only _FP_FRAC_HIGHBIT_DW_1,
_FP_FRAC_HIGHBIT_DW_2 and _FP_FRAC_HIGHBIT_DW_4 in the
soft-fp/op-*.h.

After this modification, we can pass the soft floating testing of glibc
testsuites on RV32.

	* soft-fp/op-8.h (_FP_FRAC_SET_8, _FP_FRAC_ADD_8, _FP_FRAC_SUB_8)
	(_FP_FRAC_CLZ_8, _FP_MINFRAC_8, _FP_FRAC_NEGP_8, _FP_FRAC_ZEROP_8)
	(_FP_FRAC_HIGHBIT_DW_8, _FP_FRAC_COPY_4_8, _FP_FRAC_COPY_8_4)
	(__FP_FRAC_SET_8): Add implementation for RV32 use.