xtensa: make local symbols static

Symbols that are not exported should be declared as static.

Change-Id: Ieb627f7f896e4663b0d5b18c4ab1853b39d23d03
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7167
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Reviewed-by: Ian Thompson <ianst@cadence.com>
Tested-by: jenkins

src/target/espressif/esp32s2.c

@@ -122,7 +122,7 @@ static int esp32s2_deassert_reset(struct target *target)
 	return ERROR_OK;
 }
 
-int esp32s2_soft_reset_halt(struct target *target)
+static int esp32s2_soft_reset_halt(struct target *target)
 {
 	LOG_TARGET_DEBUG(target, "begin");