ipq806x: provide ramoops for R7800/XR500 by default

Add kmod-ramoops to the default set of device packages in
R7800 and XR500, so that the ramoops kernel crash logs
are provided by default for these routers.

The capability was earlier defined by 97158fe1 and cf346dfa,
but the feature was not yet turned on by default.

The possible kernel crashes are stored into /sys/fs/pstore/*

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>