lib/thread: Add thread_yield helper method

This helper method is just a shorthand for
`thread_yield_microseconds(0)`. I think it makes it clear that we want
to yield a thread without delaying.

BUG=b:179699789
TEST=build test

Suggested-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: Id8b60c35b183cff6871d7ba70b36eb33b136c735
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56349
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/thread.c

@@ -332,6 +332,11 @@ int thread_run_until(void (*func)(void *), void *arg,
 	return 0;
 }
 
+int thread_yield(void)
+{
+	return thread_yield_microseconds(0);
+}
+
 int thread_yield_microseconds(unsigned int microsecs)
 {
 	struct thread *current;