omap_gpmc: add support for hw assisted BCH8

The kernel states:

---8<---
The OMAP3 GPMC hardware BCH engine computes remainder polynomials, it does not
provide automatic error location and correction: this step is implemented using
the BCH library.
--->8---

And we do so in u-boot.

This implementation uses the same layout for BCH8 but it is fix. The current
provided layout does only work with 64 Byte OOB.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Tom Rini <trini@ti.com>
Cc: Ilya Yanok <ilya.yanok@cogentembedded.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Mansoor Ahamed <mansoor.ahamed@ti.com>
Cc: Thomas Weber <thomas.weber.linux@googlemail.com>