archconfig.sh: Assuming BOARD value is set statically at build time
archconfig.sh: Assuming BOARD value is set statically at build time

Previously archconfig was reading BOARD and BOARD_VARIANT values and
adding to dnf configs. Now, assuming that the BOARD value is set in
configs at build time and adding BOARD_VARIANT only to configs. (there
is a quick check to confirm that BOARD is set before adding
BOARD_VARIANT, else archconfig will print a message and do nothing.

Signed-off-by: Jaewon Lee <1b369288d13b7b5cc9a37dd614e864b90fd18321@xilinx.com>

Xilinx/meta-petalinux,Xilinx/meta-petalinux,Xilinx/meta-petalinux,Xilinx/meta-petalinux,Xilinx/meta-petalinux,Xilinx/meta-petalinux