linux: Release 4.12.8-openpower1

This brings the OpenPower kernel up to the latest stable kernel release.
4.12.8 contains an important fix for Power9 DD2:

  powerpc: Fix /proc/cpuinfo revision for POWER9 DD2

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 806396a..c67f945 100644
--- a/openpower/linux/0002-Release-OpenPower-kernel.patch
+++ b/openpower/linux/0002-Release-OpenPower-kernel.patch
@@ -9,13 +9,13 @@
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/Makefile b/Makefile
-index 382e967b0792..832de374937a 100644
+index 6da481d08441..b864af3df096 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -1,7 +1,7 @@
  VERSION = 4
  PATCHLEVEL = 12
- SUBLEVEL = 5
+ SUBLEVEL = 8
 -EXTRAVERSION =
 +EXTRAVERSION = -openpower1
  NAME = Fearless Coyote