arm: zynq: Move common ps7_init* initialization to arch code

This patch is based on work done in topic board where the first address
word also storing operation which should be done. This is reducing size
of configuration data.
This patch is not breaking an option to copy default ps7_init_gpl* files
from hdf file but it is doing preparation for ps7_init* consolidation.

The patch is also marking ps7_config as weak function.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>