Makefile: Pass unknown targets through to the kernel make
Makefile: Pass unknown targets through to the kernel make

Add some convenience rules so we pass unknown targets through
to the kernel makefile. This allows you to say 'make menuconfig'
(for instance) from this directory.

Signed-off-by: Peter Maydell <313afa09ce093b19ae1dd74f57c1ebd94508584c@linaro.org>

virtualopensystems/boot-wrapper,virtualopensystems/boot-wrapper