mtd: nand: pxa3xx_nand: add register access debug

Add verbose debug for register accesses. This enables easier debugging
by following where and how hardware is stimulated, and how it answers.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>