kernel: Move to Linux 4.18.3-openpower1

Update to 4.18, and re-generate the defconfig. In addition, make the
following changes:

 - Enable EXPERT, so we can disable some things
 - Disable non-powerpc BPF decoders
 - Disable TASKSTATS
 - Disable unused syscalls
 - Set more things to be modules
 - Turn off unused network vendors

Note that CONFIG_I2C_CHARDEV=y as the module is not loaded
automatically, and without this i2cget etc. will fail.

Buildroot is updated to include support for v4.18.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/p9dsu_defconfig b/openpower/configs/p9dsu_defconfig
index 0a27dc5..e1dc84a 100644
--- a/openpower/configs/p9dsu_defconfig
+++ b/openpower/configs/p9dsu_defconfig
@@ -14,7 +14,7 @@
 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="4.17.12"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.18.3"
 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"