sim: Add bfd include path for common testsuite tools

On a host without installed libbfd, this patch fixes the following
"make check-sim" errors for both pru cross target, and native x86_64:

In file included from ../../../binutils/sim/common/sim-basics.h:131,
                 from testsuite/common/bits32m0.c:13:../../../binutils/sim/../include/gdb/callback.h:55:10: fatal error: bfd.h: No such file or directory
   55 | #include "bfd.h"
      |          ^~~~~~~

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>