Align the NuttX open(2) flag constants with the Linux asm-generic
values so that the FUSE wire protocol and other cross-platform
interfaces work without conversion.
All code that used '(flags & O_RDONLY)' as a bitmask check (always 0
now that O_RDONLY=0) has been updated to use '(flags & O_ACCMODE)'
comparisons.
The NUTTX_O_* constants in include/nuttx/fs/hostfs.h are updated to
match, and the sim hostfs open flag mapping is fixed.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>