LICENSE: Complete and clarify

This repo LICENSE file was missing:
- reference to SLA0044 used for STM32WBA binary blobs
- reference to Apache 2.0 Licnese used for dts files

Additionally, clarify the wording about the BSD-3-Clause license used
for files extracted from STM32Cube packages and the location of the
impacted files.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>