sim/rx: add some missing includes

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.