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/esp32s2.h

@@ -0,0 +1,40 @@
+/***************************************************************************
+ *   ESP32-S2 target for OpenOCD                                           *
+ *   Copyright (C) 2019 Espressif Systems Ltd.                             *
+ *   Author: Alexey Gerenkov <alexey@espressif.com>                        *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   This program is distributed in the hope that it will be useful,       *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU General Public License for more details.                          *
+ *                                                                         *
+ *   You should have received a copy of the GNU General Public License     *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ ***************************************************************************/
+
+#ifndef OPENOCD_TARGET_ESP32S2_H
+#define OPENOCD_TARGET_ESP32S2_H
+
+#include <target/xtensa/xtensa_regs.h>
+
+#define ESP32_S2_DROM_LOW   0x3f000000
+#define ESP32_S2_DROM_HIGH  0x3ff80000
+#define ESP32_S2_IROM_LOW   0x40080000
+#define ESP32_S2_IROM_HIGH  0x40800000
+
+/* Number of registers returned directly by the G command
+ * Corresponds to the amount of regs listed in regformats/reg-xtensa.dat in the gdb source */
+#define ESP32_S2_NUM_REGS_G_COMMAND   72
+
+enum esp32s2_reg_id {
+	/* chip specific registers that extend ISA go after ISA-defined ones */
+	ESP32_S2_REG_IDX_GPIOOUT = XT_USR_REG_START,
+	ESP32_S2_NUM_REGS,
+};
+
+#endif	/* OPENOCD_TARGET_ESP32S2_H */