x86/alix2: add kmod-usb2-pci to default packages

The USB controller is sitting on the PCI bus and
without the package the EHCI controller is not
usable.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37835 3c298f89-4303-0410-b956-a3cf2f4a3e73