Add Flex-OneNAND booting support

Add Flex-OneNAND booting support

Flex-OneNAND is a monolithic integrated circuit with a NAND Flash array
using a NOR Flash interface. This on-chip integration enables system designers
to reduce external system logic and use high-density NAND Flash
in applications that would otherwise have to use more NOR components.

Flex-OneNAND enables users to configure to partition it into SLC and MLC areas
in more flexible way. While MLC area of Flex-OneNAND can be used to store data
that require low reliability and high density, SLC area of Flex-OneNAND
to store data that need high reliability and high performance. Flex-OneNAND
can let users take advantage of storing these two different types of data
into one chip, which is making Flex-OneNAND more cost- and space-effective.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>