README.md: Ultra96 is compatible with v1 board
README.md: Ultra96 is compatible with v1 board

Update README stating that Ultra96 machine configuration file is
compatible with v1 board and refer to meta-avnet for v2 board.

Signed-off-by: Sandeep Gundlupet Raju <eaeca0ea0d778dfb64d22c43189d46f965ce7ff5@xilinx.com>
Signed-off-by: Mark Hatle <41765ab18fb75e64ff0efe27f2ebcdb2d6f7e44e@amd.com>

Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx