MAINTAINERS: Remove Xiaolei Li and mark MTK NFC as orphaned

Xiaolei's address is bouncing, remove him from MAINTAINERS and mark
the driver he was maintaining, Mediatek's, as orphaned.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200510211809.15610-2-miquel.raynal@bootlin.com