arm64: zynqmp: Define default SYS_PROMPT

All boards are using the same prompt that's why add it as default value to
Kconfig to simplify defconfigs.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
29 files changed