[MTD NAND] Update CS553x NAND driver: Hardware ECC support, optimisations.

- Implement HW ECC support,
- Provide read_buf() and write_buf() routines using memcpy
- Use on-flash bad block table
- Fix module refcounting
- Avoid read/modify/write in hwcontrol()
- Minor cosmetic fixes

Partly based on code and ideas from Tom Sylla <tom.sylla@amd.com>

Signed-off-by: David Woodhouse <dwmw2@infradead.org>