board: kontron: disable flash unlock all

Although the status register is protected by the hardware write
protection, there is a hardware jumper to disable that hardware write
protection. Thus if a user would set this jumper any u-boot start would
disable the write protection altogether.

Circumvent that by not disabling the write protection in the first
place.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>

configs/kontron_sl28_defconfig

@@ -73,6 +73,7 @@ CONFIG_MMC_HS400_SUPPORT=y
 CONFIG_FSL_ESDHC=y
 CONFIG_FSL_ESDHC_SUPPORT_ADMA2=y
 CONFIG_DM_SPI_FLASH=y
+# CONFIG_SPI_FLASH_UNLOCK_ALL is not set
 CONFIG_SPI_FLASH_WINBOND=y
 # CONFIG_SPI_FLASH_USE_4K_SECTORS is not set
 CONFIG_PHYLIB=y