Platform/RaspberryPi: add license header to PlatformUiAppLib.inf

PlatformUiAppLib.inf was accidentally merged without an explicit license
header. Add one that matches the actual source code (BSD+Patent, after
the general relicensing earlier this year.
(This has been OK:d with Andrei off-list.)

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>