espressif: Add ESP32-C3 initial basic support

ESP32-C3 target added to the Espressif port, CMakeLists, and
added related files to ESP32-C3 target directory as well.

Signed-off-by: Almir Okato <almir.okato@espressif.com>
diff --git a/boot/espressif/tools/toolchain-esp32c3.cmake b/boot/espressif/tools/toolchain-esp32c3.cmake
new file mode 100644
index 0000000..cd30a2a
--- /dev/null
+++ b/boot/espressif/tools/toolchain-esp32c3.cmake
@@ -0,0 +1,9 @@
+set(CMAKE_SYSTEM_NAME Generic)
+
+set(CMAKE_C_COMPILER riscv32-esp-elf-gcc)
+set(CMAKE_CXX_COMPILER riscv32-esp-elf-g++)
+set(CMAKE_ASM_COMPILER riscv32-esp-elf-gcc)
+
+set(CMAKE_C_FLAGS "-march=rv32imc" CACHE STRING "C Compiler Base Flags")
+set(CMAKE_CXX_FLAGS "-march=rv32imc" CACHE STRING "C++ Compiler Base Flags")
+set(CMAKE_EXE_LINKER_FLAGS "-nostartfiles -march=rv32imc --specs=nosys.specs" CACHE STRING "Linker Base Flags")