test: dm: Add test for fastboot mmc partition naming

This test verifies the mapping between fastboot partitions and partitions
as understood by U-Boot. It also tests the creation of GPT partitions,
though that is not the primary goal.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index a485b38..5bc90d0 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -137,6 +137,8 @@
 CONFIG_DMA=y
 CONFIG_DMA_CHANNELS=y
 CONFIG_SANDBOX_DMA=y
+CONFIG_FASTBOOT_FLASH=y
+CONFIG_FASTBOOT_FLASH_MMC_DEV=0
 CONFIG_GPIO_HOG=y
 CONFIG_DM_GPIO_LOOKUP_LABEL=y
 CONFIG_PM8916_GPIO=y