FPU: Make fsel not alter FPSCR

fsel is a move-type instruction, and hence shouldn't affect FPSCR.
Set v.writing_fpr and v.instr_done, rather than setting arith_done,
to achieve this.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

fpu.vhdl

@@ -1712,7 +1712,8 @@ begin
                 misc_sel <= "111";
                 set_r := '1';
                 re_set_result <= '1';
-                arith_done := '1';
+                v.writing_fpr := '1';
+                v.instr_done := '1';
 
             when DO_FSQRT =>
                 opsel_a <= AIN_B;