arm64: zynqmp: Move bootargs setting to Kconfig

arm64: zynqmp: Move bootargs setting to Kconfig

bootargs should be setup via Kconfig. There are still xilinx commands
which are changing command line based on bootmode which are not moved.
Moving to distro default is probably the best thing to do.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Manjukumar Matha <manjukumar.harthikote-matha@xilinx.com>