return hexadecimal dump of registers as expected by GDB

def get_register_context(self):
        """
        return hexadecimal dump of registers as expected by GDB
        """
        logging.debug("GDB getting register context")
        resp = b''
        reg_num_list = [reg.reg_num for reg in self._register_list]
        vals = self._context.read_core_registers_raw(reg_num_list)
        #print("Vals: %s" % vals)
        for reg, regValue in zip(self._register_list, vals):
            if reg.bitsize == 64:
                resp += six.b(conversion.u64_to_hex16le(regValue))
            else:
                resp += six.b(conversion.u32_to_hex8le(regValue))
            logging.debug("GDB reg: %s = 0x%X", reg.name, regValue)

        return resp