libc: Kconfig: Enable STDOUT_CONSOLE by default if NEWLIB_LIBC.

Enable stdio to work by default if Newlib is used as libc - it's
reasonable expectation that if full-fledged libc (like Newlib) is
selected, then printf() works out of the box.

Fixes: #5566

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>