mtd: spi-nor: export spi_nor_hwcaps_pp2cmd()

The function will also be used by the debugfs module.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220429102018.2361038-1-michael@walle.cc