Add license headers to meta-ewaol source files

This patch adds license disclaimers in the meta-ewaol files:
-Headers in all the source files.
-New license section in the README.

Issue-Id: SCM-2638
Signed-off-by: Hugo L'Hostis <hugo.lhostis@arm.com>
Change-Id: Ibeb28a797387e71092dd60a88bfe01f5e3000566