kernel: Move to Linux v5.1-openpower1

This also bumps buildroot to include support for the 5.1 kernel series.

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 5a4cbfd..71303fb 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 May 2019 14:57:40 +0930
+Date: Fri, 10 May 2019 16:51:56 +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 51a819544505..0d3b32e3443d 100644
+index 26c92f892d24..6e5b9f60a5db 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -2,7 +2,7 @@
  VERSION = 5
- PATCHLEVEL = 0
- SUBLEVEL = 13
+ PATCHLEVEL = 1
+ SUBLEVEL = 0
 -EXTRAVERSION =
 +EXTRAVERSION = -openpower1
  NAME = Shy Crocodile