drivers: flash: jesd216: add support for DW15 decoding

DW15 provides information on entry and exit from QSPI modes.  In
particular, it specifies whether and how the status register must be
updated for this feature.

Add a JESD216 devicetree property for the Quad Enable Requirements
value.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>