* include: Introduce elf64.h and elf.h
Added elf64.h for 64bit ELF support and moved common definitions
from elf32.h to elf.h. Also introduced Elf_xxx to be used in
common libraries such as binfmt.
* binfmt, include, modlib, module: Add support for ELF64
Elf_xxx must be used instead of Elf32_xxx to support ELF64.
To use ELF64, CONFIG_ELF_64BIT must be enabled.
* binfmt, modlib: Add support for relocate address
* arch: risc-v: Add include/elf.h
* libs: machine: Add risc-v related files.
NOTE: Currently only supports ELF64
* boards: maix-bit: Add elf and posix_spawn configurations
* boards: maix-bit: Add support for module configuration
* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
YAMAMOTO Takashi