mtd: atmel_nand: add has_pmecc member

This commit replace the usage of CONFIG_NAND_ATMEL_PMECC
by a new member called: has_pmecc. This member is directly initialise
in board specific code.

Signed-off-by: Raphaël Poggi <poggi.raph@gmail.com>
mtd: atmel_nand: fix compilation error
board: at91sam9m10g45ek: remove nand init
dts: at91sam9m10g45ek: ad nand definition
at91: gpio: add support to dts
dts: at91sam9g45: add gpio entry
dts: at91sam9m10g45ek: add nand gpio
mtd: atmel_nand: retrive pin from dts
dts: at91sam9m10g45ek: fix indent