CRIS v32: Clean up nandflash.c for ARTPEC-3 and ETRAX FS.

Clean up issues noticed by Andrew Morton:

- Use a combined struct for allocating the mtd_info and nand_chip structs
  instead of using anonymous memory as the example in
  Documentation/DocBook/mtdnand.tmpl
- Use kzalloc instead of using kmalloc/memset(0)
- Make crisv32_device_ready static.