at91: atmel_nand: extract HWECC initialization code into one function: atmel_hw_nand_init_param().

This patch
1. extract the hwecc initialization code into one function. It is a preparation for adding atmel PMECC support.
2. enable CONFIG_SYS_NAND_SELF_INIT. Which make us can configurate the ecc parameters between nand_scan_ident() and nand_scan_tail().

Signed-off-by: Josh Wu <josh.wu@atmel.com>
[fix empty newline at EOF error and move return value check into ifdef]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>