OneNAND: Add simple OneNAND SPL

This introduces small OneNAND loader, fitting into 1kB of space (smallest
possible OneNAND RAM size). Some devices equipped with such crappy chips will
use this.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Scott Wood <scottwood@freescale.com>

V2: Introduce spl_onenand_load_image() to load data from OneNAND in SPL
V3: Cleanup, align with nand_spl. Skip whole blocks.