kernel: Move to v5.10.50-openpower1

This moves the openpower platform to the v5.10 kernel. All of the secure
boot patches are now upstream, allowing them to be dropped.

The only outstanding patch is the long-lived USB kexec patch.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/opal_defconfig b/openpower/configs/opal_defconfig
index 54e39f1..882b8c5 100644
--- a/openpower/configs/opal_defconfig
+++ b/openpower/configs/opal_defconfig
@@ -1,6 +1,6 @@
 BR2_powerpc64le=y
 BR2_powerpc_power8=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_4=y
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_10=y
 BR2_BINUTILS_EXTRA_CONFIG_OPTIONS="--enable-targets=powerpc64-linux"
 BR2_EXTRA_GCC_CONFIG_OPTIONS="--enable-targets=powerpc64-linux --disable-libsanitizer"
 BR2_TARGET_GENERIC_HOSTNAME="skiroot"
@@ -13,7 +13,7 @@
 BR2_ROOTFS_POST_BUILD_SCRIPT="../openpower/scripts/fixup-target-var ../openpower/scripts/firmware-whitelist"
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.4.132"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.10.50"
 BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL_OP_BUILD_PATH)/linux"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_defconfig"