When __SINGLE_THREAD__ is not defined, stdin, stdout and stderr needs
to have their _lock instance initialized. The __sfp() method is not
invoked for the 3 mentioned fds thus, the std() method needs to handle
the initialization of the lock.
This is more or less a revert of 382550072b49430f8c69adee937a0ba07bd385e6
Contributed by STMicroelectronics
Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
dd1122e21c