Call print_insn_mep in mep_gdb_print_insn

Call print_insn_mep in mep_gdb_print_insn

opcodes/mep-dis.c:mep_print_insn has already had the code to
handle the case when info->section is NULL,

  /* Picking the right ISA bitmask for the current context is tricky.  */
  if (info->section)
    {
    }
  else /* sid or gdb */
    {
    }

so that we can still cal print_insn_mep even section can't be found.
On the other hand, user can disassemble an arbitrary address which
doesn't map to any section at all.

gdb:

2017-01-26  Yao Qi  <yao.qi@linaro.org>

	* mep-tdep.c (mep_gdb_print_insn): Set info->arch
	to bfd_arch_mep.  Don't return 0 if section is not
	found.  Call print_insn_mep.