mtd: pxa3xx_nand: Remove redundant NAND sensing

Currently, the driver is trying to detect the presence of a chip
by issuing a RESET command before nand_scan_ident. This seems completely
redundant, and is also a layering violation as nand_scan_ident is in charge
of device detection.

This commit removes the RESET command use, and moves the initial
timing configuration to pxa3xx_nand_config_ident.

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