xilinx: Define kernel_comp_addr_r,kernel_comp_size env variables

Add kernel_comp_addr_r, kernel_comp_size env variables for zynqmp and
versal to be able to use the compressed kernel Image(.gz,.bz2,.lzma,.lzo)
using booti command.

Signed-off-by: Raju Kumar Pothuraju <raju.kumar-pothuraju@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>