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/linux/0002-Release-OpenPower-kernel.patch b/openpower/linux/0002-Release-OpenPower-kernel.patch
index 57b8ccd..47b05eb 100644
--- a/openpower/linux/0002-Release-OpenPower-kernel.patch
+++ b/openpower/linux/0002-Release-OpenPower-kernel.patch
@@ -1,6 +1,6 @@
 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
 From: Joel Stanley <joel@jms.id.au>
-Date: Mon, 6 Aug 2018 09:57:08 +0930
+Date: Mon, 20 Aug 2018 11:13:08 +0930
 Subject: [PATCH 2/2] Release OpenPower kernel
 
 Signed-off-by: Joel Stanley <joel@jms.id.au>
@@ -9,13 +9,13 @@
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/Makefile b/Makefile
-index 790e8faf0ddc..50a44b3512dc 100644
+index e2bd815f24eb..8ee63eaae1b9 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -2,7 +2,7 @@
  VERSION = 4
- PATCHLEVEL = 17
- SUBLEVEL = 12
+ PATCHLEVEL = 18
+ SUBLEVEL = 3
 -EXTRAVERSION =
 +EXTRAVERSION = -openpower1
  NAME = Merciless Moray