ARM: dts: da850-evm: Use generic jedec, spi-nor for flash

Logic PD re-spun the L138 and AM1808 SOM's with larger flash.
The m25p80 driver has a generic 'jedec,spi-nor' compatible option
which is requests to use whenever possible since it will read the
JEDEC READ ID opcode.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>