qemu: common: Set dfu_alt_info variable for the platform

The dfu framework uses the dfu_alt_info environment variable to get
information that is needed for performing the firmware update. Add
logic to set the dfu_alt_info for the qemu arm64 platform to reflect
the two mtd partitions created for the u-boot env and the firmware
image. This can be subsequently extended for other qemu architectures
which need this variable set.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
diff --git a/board/emulation/qemu-arm/Kconfig b/board/emulation/qemu-arm/Kconfig
index 0108efe..fb8d38f 100644
--- a/board/emulation/qemu-arm/Kconfig
+++ b/board/emulation/qemu-arm/Kconfig
@@ -15,6 +15,7 @@
 if TARGET_QEMU_ARM_64BIT && !TFABOOT
 config BOARD_SPECIFIC_OPTIONS
 	imply SYS_MTDPARTS_RUNTIME
+	imply SET_DFU_ALT_INFO
 
 source "board/emulation/common/Kconfig"
 endif