configs/wandboard: bump kernel and U-Boot versions

- Bump kernel to version 5.12.2.
- Bump U-Boot to version 2021.04.

While at it, switch U-Boot to the Kconfig build system and add some more
comments to the defconfig.

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/wandboard_defconfig

@@ -1,32 +1,46 @@
+# Architecture
 BR2_arm=y
 BR2_cortex_a9=y
 BR2_ARM_ENABLE_NEON=y
 BR2_ARM_ENABLE_VFP=y
 BR2_ARM_FPU_VFPV3=y
-# Linux headers same as kernel, a 5.10 series
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_10=y
+
+# Linux headers same as kernel, a 5.12 series
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_12=y
+
+# System
 BR2_TARGET_GENERIC_GETTY_PORT="ttymxc0"
+
+# Image
 BR2_ROOTFS_POST_BUILD_SCRIPT="board/wandboard/post-build.sh"
 BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh"
 BR2_ROOTFS_POST_SCRIPT_ARGS="-c board/wandboard/genimage.cfg"
+
+# Filesystem
 BR2_TARGET_ROOTFS_EXT2=y
 BR2_TARGET_ROOTFS_EXT2_4=y
+
+# Bootloader
 BR2_TARGET_UBOOT=y
-BR2_TARGET_UBOOT_BOARDNAME="wandboard"
+BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION=y
-BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2021.01"
+BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2021.04"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="wandboard"
 BR2_TARGET_UBOOT_FORMAT_IMG=y
 BR2_TARGET_UBOOT_SPL=y
 BR2_TARGET_UBOOT_SPL_NAME="SPL"
+
+# Kernel
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.10.9"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.12.2"
 BR2_LINUX_KERNEL_DEFCONFIG="imx_v6_v7"
 BR2_LINUX_KERNEL_DTS_SUPPORT=y
 BR2_LINUX_KERNEL_INTREE_DTS_NAME="imx6q-wandboard imx6dl-wandboard imx6q-wandboard-revb1 imx6dl-wandboard-revb1 imx6q-wandboard-revd1 imx6dl-wandboard-revd1 imx6qp-wandboard-revd1"
 BR2_LINUX_KERNEL_INSTALL_TARGET=y
 BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
-# required tools to create the SD card image
+
+# Required tools to create the SD image
 BR2_PACKAGE_HOST_DOSFSTOOLS=y
 BR2_PACKAGE_HOST_GENIMAGE=y
 BR2_PACKAGE_HOST_MTOOLS=y