linux-mainline: removed defconfig override

Was used to debug why the kernel config overrides weren't being handled
by bitbake. Resolved, so now just using config fragments.

Signed-off-by: Mike Lewis <mikelewis@alphalem.com>
Added u-boot beagleboard recipe and support files

Starting point for AlphaOne u-boot work.

Signed-off-by: Mike Lewis <mikelewis@alphalem.com>