cmd: mvebu/bubt: Better guess default MVEBU_*_BOOT option

For 32-bit Armada boards which use SPL we can determinate boot device from
existing MVEBU_SPL_BOOT_DEVICE_* option. For all other boards (e.g. 64-bit
Armada) default option still needs to be set manually.

Signed-off-by: Pali Rohár <pali@kernel.org>
diff --git a/cmd/mvebu/Kconfig b/cmd/mvebu/Kconfig
index 9f6ad2d..029f722 100644
--- a/cmd/mvebu/Kconfig
+++ b/cmd/mvebu/Kconfig
@@ -18,6 +18,10 @@
 
 choice
 	prompt "Flash for image"
+	default MVEBU_SPI_BOOT if MVEBU_SPL_BOOT_DEVICE_SPI
+	default MVEBU_NAND_BOOT if MVEBU_SPL_BOOT_DEVICE_NAND
+	default MVEBU_MMC_BOOT if MVEBU_SPL_BOOT_DEVICE_MMC
+	default MVEBU_SATA_BOOT if MVEBU_SPL_BOOT_DEVICE_SATA
 	default MVEBU_SPI_BOOT
 
 config MVEBU_NAND_BOOT