Cache options must be enabled for the cores that have cache to avoid
illegal instruction exceptions.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

Introduce overlay_tool.h that defines core configuration blocks from
data available in the linux architecture variant overlay.

Overlay data is automatically generated in the core configuration
process by Tensilica tools and can be directly converted to qemu xtensa
core description by overlay_tool.h
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>