mtd: pxa3xx_nand: Fix initial controller configuration

The Data Flash Control Register (NDCR) contains two types
of parameters: those that are needed for device identification,
and those that can only be set after device identification.

Therefore, the driver can't set them all at once and instead
needs to configure the first group before nand_scan_ident()
and the second group later.

Let's split pxa3xx_nand_config in two halves, and set the
parameters that depend on the device geometry once this is known.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>