sim/rx: add some missing includes

In load.c there's some GCC warnings about undefined
functions (bfd_get_elf_phdr_upper_bound and bfd_get_elf_phdrs).  To
get the declarations of these functions include 'elf-bfd.h'.  This
headers also pulls in other elf related headers, like 'elf/internal.h'
and 'elf/common.h', so these no longer need to be explicitly included
from load.c.

In trace.c and include for trace.h is missing, again this results in
GCC warnings for missing function declarations.

sim/rx/ChangeLog:

	* load.c: Replace 'elf/internal.h' and 'elf/common.h' includes
	with 'elf-bfd.h' include.
	* trace.c: Add 'trace.h' include.

sim/rx/trace.c

@@ -34,6 +34,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "cpu.h"
 #include "mem.h"
 #include "load.h"
+#include "trace.h"
 
 static int
 sim_dis_read (bfd_vma memaddr, bfd_byte * ptr, unsigned int length,