mtd: spi-nor: cadence-quadspi: Add TI 66AK2G SoC specific compatible

Update binding documentation to add a new compatible for TI 66AK2G SoC,
to handle TI SoC specific quirks in the driver.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>