checkpatch: add --typedefsfile

checkpatch: add --typedefsfile

When using checkpatch on out-of-tree code, it may occur that some
project-specific types are used, which will cause spurious warnings.
Add the --typedefsfile option as a way to extend the known types and
deal with this issue.

This was developed for OP-TEE [1].  We run a Travis job on all pull
requests [2], and checkpatch is part of that.  The typical false warning
we get on a regular basis is with some pointers to functions returning
TEE_Result [3], which is a typedef from the GlobalPlatform APIs.  We
consider it is acceptable to use GP types in the OP-TEE core
implementation, that's why this patch would be helpful for us.

[1] https://github.com/OP-TEE/optee_os
[2] https://travis-ci.org/OP-TEE/optee_os/builds
[3] https://travis-ci.org/OP-TEE/optee_os/builds/193355335#L1733

Link: http://lkml.kernel.org/r/ba1124d6dfa599bb0dd1d8919dd45dd09ce541a4.1492702192.git.jerome.forissier@linaro.org
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Cc: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>