ARM: dts: armada388-clearfog: enable spi flash

The SolidRun Armada 388 SOM has the SPI flash populated by default
unless the customer explicitly asks otherwise. Enable support by
default.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>