[FIX] Fix compilation issue in edrv-8255x

During merging of develop-2.0 some variables were not
correctly renamed.

Change-Id: Ic5c1cdef6f707f4ababe6b4fa674ff5dccf8c070
[TASK] Add Zynq SoC platform documentation

- Add platform documentation for Zynq SoC.
- Update build steps for demos, drivers, hardware and stack
  to compile it for target Xilinx ARM.

Change-Id: I62a2da8fbf8bd11585b840dbec74304e801a5517
Signed-off-by: Joerg Zelenka <joerg.zelenka@br-automation.com>
Signed-off-by: Josef Baumgartner <josef.baumgartner@br-automation.com>
[TASK] Clean up demo application system helper functions

* Add the module prefix "system_" to all system-related functions
* Group and guard functions only used with CONFIG_USE_SYNCTHREAD
* Declare private functions as static

Change-Id: Ia1eb19085d1dd2f2c726893ab18ef069aaadd93d