In case newlib is enabled, but POSIX subsys isn't, there're adhoc
implementations of read() and write() which work only with adhoc
stdin/stdout emulation layer. These are backed by system calls named
like "read" and "write". Rename all these functions and syscalls to
explicitly mention stdin/stdout in the names, to free namespace
for the implementation of generic read/write syscalls which will
integrate with POSIX fdtable.
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>