CRIS v32: Update kernel/head.S

- Shorten include paths for machine specific header files.
- Add magic for booting NAND flash.
- Change CONFIG_ETRAXFS_SIM to CONFIG_ETRAX_VCS_SIM.
- Use assembler macros for initializing hardware (clocks)
- Add stubs for SMP slave CPUs.
- Search for cramfs or jffs2 if no romfs found.
- Initialize l2cache.