ANDROID: trusty: fix up headers shared with Trusty

Consistently use the MIT license for headers that are also duplicated in
Trusty (and sometimes in TF-A too).  This is the license in the other
copies, and unlike GPL-2.0 it's compatible with both Linux and Trusty.

For trusty-log.h, also add the copyright statement that is in the other
copy, as the MIT license requires a copyright statement.

Also remove the unnecessary include of <linux/bits.h> in arm_ffa.h.

Finally, also add reminders to keep the headers in sync.

Change-Id: Id0349d605013a941d2c54d9a372991b300d8feea
Signed-off-by: Eric Biggers <ebiggers@google.com>