Add LICENSE file

The manifest file already contains the text of the license for this
project. Include a plain-text license file explicitly as well.

Cc: Nishanth Menon <nm@ti.com>
Cc: Praneeth Bajjuri <praneeth@ti.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>