A couple of issues are resolved by moving to the mainline kernel (from Pali's
kernel):
1) 'reboot' command now works as intended
2) boot is *much* faster
3) charging LED seems to be working now
This removes the call to `firmware_install` in the APKGBUILD for
linux-nokia-rx51, and adds the `linux-firmware` package as a dependency
for device-nokia-rx51.
There are two immediate benefits for this:
1) wifi now works
2) the FM radio device was causing the boot to take ~2 minutes longer
than it should, now that the firmware is present there's no delay in
initializing this device
