fix(eclass/cros-kernel2.eclass) version the debug kernel

The debug kernel image needs to be versioned, like the rest of the
kernel files, so that multiple kernels can be installed at the same
time.  So put it into a unique directory.
fix(sys-kernel/coreos-kernel) no more firmware files

The kernel package should not be building any firmware files, as they
are not needed in virtual machines, _and_ the firmware file locations
are not versioned, preventing multiple kernels to be installed at the
same time.

This change adds a patch to the kernel to not traverse into the firmware
directory at all, and patches the eclass to not do the firmare_install
build process.