ext: hal: altera: Don't depend on NEWLIB_LIBC

Contrary to what was written in its Kconfig, hal/altera depends not
on Newlib, but on a baseline POSIXish define like O_NONBLOCK. Minimal
libc now provides them, so there're no issues with building Altera
for either minimal on newlib libc.

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