ColdFire: Fix M5329EVB and M5373EVB nand issue

Fix compilation issue caused by a few mismatches.
Provide proper nand chip select enable/disable in
nand_hwcontrol() rather than in board_nand_init()
just enable once. Remove redundant local nand driver
functions - nand_read_byte(), nand_write_byte() and
nand_dev_ready() to use common nand driver.

Signed-off-by: TsiChung Liew <Tsi-Chung.Liew@freescale.com>