mtd: nand: denali: max_banks calculation changed in revision 5.1

Read Denali hardware revision number and use it to
calculate max_banks,  The encoding of max_banks changed
in Denali revision 5.1.

[ Linux commit : 271707b1d817f5104e02b2bd1bab43f0c8759418 ]

Signed-off-by: Graham Moore <grmoore@opensource.altera.com>
[Brian: parentheses around macro arg]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
[Masahiro: import from Linux and adjust ioread32() to readl() ]
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>