Documentation: migrate README.txt from boards and fixes for mps boards

migrate some README.txt form boards/ and fixes for mps boards rst

Documentation/platforms/risc-v/hpm6000/boards/hpm6360evk/index.rst

@@ -0,0 +1,47 @@
+==========
+hpm6360evk
+==========
+
+1. Download and install toolchain::
+
+     curl https://github.com/hpmicro/riscv-gnu-toolchain/releases/tag/2022.05.15
+
+2. Download and install openocd.
+
+  Download hpmicro sdk_env, openocd in the path: sdk_env/tools/openocd
+
+3. Configure and build NuttX::
+
+     mkdir ./nuttxspace
+     cd ./nuttxspace
+     git clone https://github.com/apache/nuttx.git nuttx
+     git clone https://github.com/apache/nuttx-apps.git apps
+     cd nuttx
+     make distclean
+     ./tools/configure.sh hpm6750evk2:nsh
+     make menuconfig
+     make V=1
+
+Note: make menuconfig to config toolchain
+
+To switch GNU riscv64 toolchain to GNU riscv32 toolchain, the following option must be selected::
+
+    System Type  --->
+        Toolchain Selection   --->
+            [ ] Generic GNU RV64 toolchain
+            [x] Generic GNU RV32 toolchain
+
+Make sure HPMicro GNU riscv32 toolchain have been installed and be found in PATH.
+
+4. Debug the nuttx with openocd and run::
+
+     picocom -b 115200 /dev/ttyACM0
+
+  When using fireDAP, command as follows. Those cfg files in the path: ``sdk_env/hpm_sdk/boards/openocd``::
+
+    $ openocd -f probes/cmsis_dap.cfg -f soc/hpm6750-single-core.cfg -f boards/hpm6750evk2.cfg
+
+    $ riscv32-unknown-elf-gdb ./nuttx
+    (gdb) target extended-remote [ip_addr]:3333
+    (gdb) load
+    (gdb) c

Documentation/platforms/risc-v/hpm6000/index.rst

@@ -0,0 +1,12 @@
+===============
+Hpmicro HPM6000
+===============
+
+Supported Boards
+================
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   boards/*/*