mtd: spinand: use the spi-mem poll status APIs

Make use of spi-mem poll status APIs to let advanced controllers
optimize wait operations.
This should also fix the high CPU usage for system that don't have
a dedicated STATUS poll block logic.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20210518162754.15940-3-patrice.chotard@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>