Convert to SPDX license tags

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

Trivial: style fix

make the style checker happy

Fix licenses

Fix licenses

libsel4vchan: replace <linux/types.h> with <stddef.h>

Fix compilation with GCC 5.0

Remove duplicate macro definitions of min() and max();
change type of _remaining_ from size_t to int to avoid type clashing;
and fix the type signature mismatch from wait_for_event() and
event_thread_info(), etween prototype and implementation.