mtd: nand: pxa3xx: Move cached registers to info structure

This registers are not per-chip (aka host) but controller-wide,
so it's better to store them in the global 'info' structure.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>