target: add generic Xtensa LX support

Generic Xtensa LX support extends the original Espressif/Xtensa
patch-set to support arbitrary Xtensa configurations, as defined in
a core-specific .cfg file.  Not yet fully-featured.  Additional
functionality to be added:
- Xtensa NX support
- DAP/SWD support
- File-IO support
- Generic Xtensa multi-core support

Valgrind-clean, no new Clang analyzer warnings

Signed-off-by: Ian Thompson <ianst@cadence.com>
Change-Id: I08e7bf8fa57c25b5d0cb75a1aa7a2ac13a380c52
Reviewed-on: https://review.openocd.org/c/openocd/+/7055
Tested-by: jenkins
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/target.c

@@ -77,6 +77,7 @@ extern struct target_type fa526_target;
 extern struct target_type feroceon_target;
 extern struct target_type dragonite_target;
 extern struct target_type xscale_target;
+extern struct target_type xtensa_chip_target;
 extern struct target_type cortexm_target;
 extern struct target_type cortexa_target;
 extern struct target_type aarch64_target;
@@ -118,6 +119,7 @@ static struct target_type *target_types[] = {
 	&feroceon_target,
 	&dragonite_target,
 	&xscale_target,
+	&xtensa_chip_target,
 	&cortexm_target,
 	&cortexa_target,
 	&cortexr4_target,