ARM: zynq: Increase init ram size by 4K

Increase init ram size by 4K such that more stack space will be available
during initialization as the present stackspace is not sufficient if DEBUG
option is enabled and causes system hang. Increasing init ram size provides
sufficient stack space during init even if DEBUG enabled and solves the
hang issue.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>