mtd: rawnand: stm32_fmc2: Add NAND Write Protect support

This patch adds the support of the WP# signal. WP will be disabled in
probe/resume callbacks and will be enabled in remove/suspend callbacks.

Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220217144755.270679-3-christophe.kerello@foss.st.com