ARM DaVinci: EMIF settings

NAND module should not modify EMIF registers unrelated to CS2
that is used for NAND, i.e. do not modify EWAIT config register
or registers for other Chip Selects.

Without this patch, EMIF configurations made in board_init()
will be invalidated.

Signed-off-by: Thomas Lange <thomas@corelatus.se>