xilinx: versal: Fix compilation error when !CONFIG_NET

PXE and DHCP shouldn't be listed when commands are not enabled that's why
handle it in the same way as is done for Zynq and ZynqMP.

Fixes: ec48b6c9 ("arm64: versal: Add support for new Xilinx Versal ACAPs")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>