documentation: description of core/include/
documentation: description of core/include/

Add missing description of the file-tree content of directory
core/include.

Sub-directory core/include/dt-bindings is mentioned even if
currently empty as it is where the device tree bindings header
files should be located.

Remove deprecated core/arch/user_mode description.

Signed-off-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@linaro.org>
Reviewed-by: Jerome Forissier <ced78d268b4c9a0a20a59a9feeebd2ad90da03d3@linaro.org>
Acked-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os