boot/arm-trusted-firmware: licensing info is only valid for v1.4

The licensing information, and especially the name of the license file,
is known only for the official v1.4 version. For example, in later
versions, the license file has been renamed.

Since we can't be sure of the licensing information for custom versions,
or for versions from git, define that only for the known v1.4 version.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Adam Duskett <aduskett@gmail.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>