packagegroups: Move inheriting packagegroup after setting PACKAGE_ARCH

Fixes

ERROR: Please ensure recipe
/home/ubuntu/work/angstrom/sources/meta-opie/recipes-opie/packagegroups/packagegroup-opie-16mb.bb
sets PACKAGE_ARCH before inherit packagegroup
ERROR: Please ensure recipe
/home/ubuntu/work/angstrom/sources/meta-opie/recipes-opie/packagegroups/packagegroup-opie.bb
sets PACKAGE_ARCH before inherit packagegroup

Signed-off-by: Khem Raj <raj.khem@gmail.com>