target/riscv: rationalise softfloat includes

We should avoid including the whole of softfloat headers in cpu.h and
explicitly include it only where we will be calling softfloat
functions. We can use the -types.h and -helpers.h in cpu.h for the few
bits that are global.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Palmer Dabbelt <palmer@sifive.com>

target/riscv/fpu_helper.c

@@ -21,6 +21,7 @@
 #include "qemu/host-utils.h"
 #include "exec/exec-all.h"
 #include "exec/helper-proto.h"
+#include "fpu/softfloat.h"
 
 target_ulong riscv_cpu_get_fflags(CPURISCVState *env)
 {