drivers: mtd: m25p80: add quad read support

Some flash also support quad read mode. Adding support for quad read
mode in m25p80 for Spansion and Macronix flash.

[Tweaked by Brian]

With this patch, quad-read support will override fast-read and
normal-read, if the SPI controller and flash chip both support it.

Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Tested-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>