mtd: spi-nor-core: Add the ->ready() hook

For dual/quad die package devices from Spansion/Cypress, the device's
status needs to be checked by reading status registers in all dies, by
using Read Any Register command. To support this, a Flash specific hook
that can overwrite the legacy status check is needed.

Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>