arm64: zynqmp: Use zynqmp_virt platform

Decrease amount of the similar defconfigs and use generic one instead.
The change was declared by commit 4b37c13d
("arm64: zynqmp: Introduce virtual defconfig") and this patch removes
configs for the most of the boards.
Utra96/zcu100/zcu102/zcu102 and ZynqMP based System controllers *a2197*.
have been also boot tested to make sure that funcionality
remains the same.

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