ARM: OMAP2+: gpmc: fix gpmc_hwecc_bch_capable()

This patch adds bch8 ecc software fallback which is mostly used by
omap3s because they lack hardware elm support.

Fixes: 0611c419 (ARM: OMAP2+: gpmc:
update gpmc_hwecc_bch_capable() for new platforms and ECC schemes)
Cc: <stable@vger.kernel.org> # 3.15.x+
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Reviewed-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>