mtd: nand: pl35x: Implement De-select in Chip Select which saves power

mtd: nand: pl35x: Implement De-select in Chip Select which saves power

nand_select_chip when called with negative chip no.
means we have finished operations on the chip
so we can deselect it. This allows the chip to
enter a lower power state.

Signed-off-by: Andrew Worsley <amworsley@gmail.com>
Reviewed-by: Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>