mtd: spi-nor: Enable QE bit for ISSI flash

Enable QE bit for ISSI flash chips.

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

Cc: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>