[MTD] NAND nandsim: Use NAND_SKIP_BBT option

Use the new NAND_SKIP_BBT option instead of defining a fake scan_bbt
handler.

Signed-off-by: Artem B. Bityuckiy <dedekind@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>