Enable 8bit interface on HSMMC2 for am43xx to support 8bit eMMC chips.

Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Signed-off-by: NNikita Kiryanov <nikita@compulab.co.il>