ARM: OMAP: gpmc: enable hwecc for AM33xx SoCs

The am33xx is capable of handling bch error correction modes, so
enable that feature in the driver.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Tony Lindgren <tony@atomide.com>