payloads/U-Boot: Upgrade from U-Boot "v2021.07" to "v2023.07"

U-Boot v2023.07 was released on Mon 10 July 2023.
https://source.denx.de/u-boot/u-boot/-/blob/master/doc/develop/release_cycle.rst#id5

Change-Id: Ie1c6f83bd12e959c29fad1b121c85eb0cf898e24
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/71065
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/payloads/external/U-Boot/Kconfig b/payloads/external/U-Boot/Kconfig
index 06b4b73..ccd8006 100644
--- a/payloads/external/U-Boot/Kconfig
+++ b/payloads/external/U-Boot/Kconfig
@@ -7,14 +7,14 @@
 
 config UBOOT_STABLE_COMMIT_ID
 	string
-	default "v2021.07"
+	default "v2023.07"
 
 choice
 	prompt "U-Boot version"
 	default UBOOT_STABLE
 
 config UBOOT_STABLE
-	bool "v2021.07"
+	bool "v2023.07"
 	help
 	  Stable U-Boot version