This PR adds support for PINE64 Ox64 64-bit RISC-V SBC, based on Bouffalo Lab BL808 SoC (T-Head C906 Core). Most of the code is derived from NuttX for Star64 JH7110. The source files are explained in the articles here: https://github.com/lupyuen/nuttx-ox64
### Modified Files
`boards/Kconfig`: Added Ox64 board
### New Files in boards/risc-v/bl808/ox64
`src/bl808_appinit.c`: Startup Code
`include/board.h`: Ox64 Definitions
`include/board_memorymap.h`: Memory Map
`src/etc/init.d/rc.sysinit`, `rcS`: Startup Script
`src/.gitignore`: Ignore the tmp filesystem
`scripts/ld.script`: Linker Script
`scripts/Make.defs`: Ox64 Makefile
`src/Makefile`: Ox64 Makefile
`Kconfig`: Ox64 Config
`configs/nsh/defconfig`: Build Config for `ox64:nsh`
### Updated Documentation
`platforms/risc-v/bl808/index.rst`: New page for Bouffalo Lab BL808 SoC
`platforms/risc-v/bl808/boards/ox64/index.rst`: Building and booting NuttX for Ox64
`platforms/risc-v/jh7110/boards/star64/index.rst`: Fix typo
87c1b81857