mtd: spi-nor: Enable QE bit for ISSI flash in case of SFDP

Enable QE bit for ISSI flash chips.

QE enablement logic is similar to what Macronix
has, so reuse the existing code itself.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>