board/visionfive2: enable u-boot

Enables U-Boot and required OpenSBI builds for the VisionFive2. Changes
the sdcard.img to use GPT and adds the SPL and U-Boot to partitions
specified in U-Boot's documentation for the board:

https://docs.u-boot.org/en/v2024.01/board/starfive/visionfive2.html

U-Boot config uses BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME with value
"u-boot.itb". Using BR2_TARGET_UBOOT_FORMAT_ITB fails, because the
build does not support u-boot.itb make target.

Signed-off-by: Lukasz Tekieli <tekieli.lukasz@gmail.com>
[Peter: document boot mode setting, add U-Boot documentation link]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/visionfive2/genimage.cfg

@@ -2,20 +2,22 @@
 
 image sdcard.img {
 	hdimage {
+		partition-table-type = "gpt"
 	}
 
-	# u-boot is hard coded to look at 3rd partition
-	partition dummy1 {
-		size = 512
+	partition spl {
+		partition-type-uuid = 2E54B353-1271-4842-806F-E436D6AF6985
+		image = "u-boot-spl.bin.normal.out"
 	}
 
-	partition dummy2 {
-		size = 512
+	partition uboot {
+		partition-type-uuid = BC13C2FF-59E6-4262-A352-B275FD6F7172
+		image = "u-boot.itb"
 	}
 
 	partition rootfs {
-		partition-type = 0x83
+		partition-type-uuid = 0FC63DAF-8483-4772-8E79-3D69D8477DE4
+		bootable = true
 		image = "rootfs.ext4"
-		bootable = "true"
 	}
 }

board/visionfive2/readme.txt

@@ -27,6 +27,10 @@ Preparing the board
 
 Connect a TTL UART cable to pin 6 (GND), 8 (TX) and 10 (RX).
 
+Change the boot mode pins to SD card booting (RGPIO_0=1, GRPIO_1=0):
+
+https://doc-en.rvspace.org/VisionFive2/Quick_Start_Guide/VisionFive2_SDK_QSG/boot_mode_settings.html
+
 Insert your SD card.
 
 Power-up the board using an USB-C cable.