target/xtensa: enable xtensa algo support

- Add extra error checking
- Cache PS; lower PS.INTLEVEL to allow  breakpoint trigger (LX)
- Xtensa algo support functional on LX per functional flash driver
- Test on NX via manual algo validation

Change-Id: Ie7cff4933979a0551308b382fa33c33c66376f25
Signed-off-by: ianst <ianst@cadence.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8075
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Tested-by: jenkins

src/target/xtensa/xtensa.h

@@ -228,8 +228,9 @@ struct xtensa_sw_breakpoint {
 struct xtensa_algorithm {
 	/** User can set this to specify which core mode algorithm should be run in. */
 	enum xtensa_mode core_mode;
-	/** Used internally to backup and restore debug_reason. */
+	/** Used internally to backup and restore core state. */
 	enum target_debug_reason ctx_debug_reason;
+	xtensa_reg_val_t ctx_ps;
 };
 
 #define XTENSA_COMMON_MAGIC 0x54E4E555U