target-xtensa: fix gdb register map construction

Due to different gdb overlay organization between windowed/call0
configurations core import script doesn't always work correctly.
Simplify the script: always copy complete gdb register map from overlay,
count registers at core registerstion time. Update existing cores.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/target-xtensa/cpu.h b/target-xtensa/cpu.h
index b592efb..b89c602 100644
--- a/target-xtensa/cpu.h
+++ b/target-xtensa/cpu.h
@@ -400,6 +400,7 @@
 void xtensa_translate_init(void);
 void xtensa_breakpoint_handler(CPUState *cs);
 int cpu_xtensa_exec(CPUXtensaState *s);
+void xtensa_finalize_config(XtensaConfig *config);
 void xtensa_register_core(XtensaConfigList *node);
 void check_interrupts(CPUXtensaState *s);
 void xtensa_irq_init(CPUXtensaState *env);