package/freescale-imx/firmware-imx: bump version to 8.15

New version contains updated binaries which are part of the NXP
5.15.5-1.0.0 Yocto release.

Update the license hashes for formatting changes and addition of
LC3plus/T2/Bluetooth SIG licenses.

Signed-off-by: Bram Vlerick <bram.vlerick@openpixelsystems.org>
[Peter: add SCR.txt license file as suggested by Stefan Hager]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>