bcm968380gerg: disable SPI_FLASH

The board bcm968380gerg don't have a spi flash so
we disable the spi flash support.
Signed-off-by: NPhilippe Reynes <philippe.reynes@softathome.com>

configs/bcm968380gerg_ram_defconfig

@@ -34,8 +34,6 @@ CONFIG_DM_GPIO=y
 CONFIG_LED=y
 CONFIG_LED_BCM6328=y
 CONFIG_LED_BLINK=y
-CONFIG_SPI_FLASH=y
-# CONFIG_SPI_FLASH_USE_4K_SECTORS is not set
 CONFIG_PHY=y
 CONFIG_BCM6368_USBH_PHY=y
 CONFIG_PINCTRL=y