gdb_server, target: Add target_address_bits()

Targets can use this to expose how many address bits there are.
gdb_server uses this to send gdb the appropriate upper limit in the
memory-map. (Before this change the upper limit would only be correct
for 32-bit targets.)

Change-Id: Idb0933255ed53951fcfb05e040674bcdf19441e1
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: http://openocd.zylin.com/4947
Tested-by: jenkins
Reviewed-by: Peter Mamonov <pmamonov@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/target/riscv/riscv.c

@@ -1560,6 +1560,11 @@ const struct command_registration riscv_command_handlers[] = {
 	COMMAND_REGISTRATION_DONE
 };
 
+unsigned riscv_address_bits(struct target *target)
+{
+	return riscv_xlen(target);
+}
+
 struct target_type riscv_target = {
 	.name = "riscv",
 
@@ -1594,7 +1599,9 @@ struct target_type riscv_target = {
 
 	.run_algorithm = riscv_run_algorithm,
 
-	.commands = riscv_command_handlers
+	.commands = riscv_command_handlers,
+
+	.address_bits = riscv_address_bits
 };
 
 /*** RISC-V Interface ***/