mtd: zynq: nand: Move board_nand_init() function to board.c

mtd: zynq: nand: Move board_nand_init() function to board.c

Putting board_nand_init() function inside NAND driver was not appropriate
due to it doesn't allow board vendor to customise their NAND
initialization code such as adding NAND lock/unlock code.

This commit was to move the board_nand_init() function from NAND driver
to board.c file. This allow customization of board_nand_init() function.

Signed-off-by: Wilson Lee <[email protected]>
Cc: Joe Hershberger <[email protected]>
Cc: Keng Soon Cheah <[email protected]>
Cc: Chen Yee Chew <[email protected]>
Cc: Albert Aribaud <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Siva Durga Prasad Paladugu <[email protected]>
Cc: Scott Wood <[email protected]>
Signed-off-by: Michal Simek <[email protected]>