The following files didn't have any copyright or license headers on them
when they got contributed. So add the SPDX Apache license and
appropriate copyright info:
boards/arm/stm32l476g_disco/pinmux.c
samples/basic/threads/src/main.c
tests/net/socket/tcp/src/main.c
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>