- Add LICENSE file specifying the 3-Clause BSD License
- update wtmi/Makefile and wtmi/clock.h from GPL to bsd-3-clause
  (it is derived from Marvell's Makefile that has been relicensed in
  Marvell's upstream)
- drop Marvell's GPL notice in wtmi/mbox.h (the file is completely
  different from Marvell's one), making it subject to bsd-3-clause
- drop Marvell's GPL notice in wtmi/types.h (Marvell licenses whole
  project under bsd-3-clause but this one file with GPL, which doesn't
  make sense, and this file has no complexity anyway), making it subject
  to bsd-3-clause

Signed-off-by: Marek Behún <marek.behun@nic.cz>