target: add Espressif ESP32-S2 basic support

ESP32-S2 is a single core Xtensa chip.
Not full featured yet. Some of the missing functionality:
-Semihosting
-Flash breakpoints
-Flash loader
-Apptrace
-FreeRTOS

Signed-off-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Change-Id: I2fb32978e801af5aa21616c581691406ad7cd6bb
Reviewed-on: https://review.openocd.org/c/openocd/+/6940
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Ian Thompson <ianst@cadence.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

src/target/espressif/Makefile.am

@@ -0,0 +1,6 @@
+noinst_LTLIBRARIES += %D%/libespressif.la
+%C%_libespressif_la_SOURCES = \
+       %D%/esp_xtensa.c \
+       %D%/esp_xtensa.h \
+       %D%/esp32s2.c \
+       %D%/esp32s2.h