Change in coreboot[master]: thread: Add thread_handle

[Raul Rangel (Code Review)]

Attention is currently required from: Julius Werner, Eric Peers, Felix Held.
Hello build bot (Jenkins), Julius Werner, Felix Held,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/56229

to look at the new patch set (#4).

Change subject: thread: Add thread_handle
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thread: Add thread_handle

The thread_handle can be used to wait for a thread to exit. I also added
a return value to the thread function that will be stored on the handle
after it completes. This makes it easy for the callers to check if the
thread completed successfully or had an error. The wait_for_thread
method uses the handle to block until the thread completes.

BUG=b:179699789
TEST=See thread_handle state update and see error code set correctly.

Signed-off-by: Raul E Rangel 
Change-Id: Ie6f64d0c5a5acad4431a605f0b0b5100dc5358ff
---
M src/include/thread.h
M src/lib/thread.c
2 files changed, 87 insertions(+), 24 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/29/56229/4