kernel: Move to Linux v5.1.15-openpower1

Powerpc related changes:

 powerpc/mm/64s/hash: Reallocate context ids on fork
 powerpc/bpf: use unsigned division instruction for 64-bit operations
 powerpc/powernv: Return for invalid IMC domain
 powerpc/64s: Fix THP PMD collapse serialisation

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch b/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
index 5982f23..d25646e 100644
--- a/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
+++ b/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
@@ -14,7 +14,7 @@
  1 file changed, 1 insertion(+)
 
 diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
-index 448e3f812833..3eb119e6f58b 100644
+index f39ca3980e48..bd7011c1ad34 100644
 --- a/drivers/usb/host/xhci.c
 +++ b/drivers/usb/host/xhci.c
 @@ -793,6 +793,7 @@ static void xhci_shutdown(struct usb_hcd *hcd)
diff --git a/openpower/linux/0002-Release-OpenPower-kernel.patch b/openpower/linux/0002-Release-OpenPower-kernel.patch
index 3d6ede6..48feb75 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: Tue, 11 Jun 2019 12:42:50 +0930
+Date: Tue, 25 Jun 2019 14:32:27 +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 3027a0ce7a02..36f60a9cff05 100644
+index d7b3c8e3ff3e..0b8b4ae447bc 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -2,7 +2,7 @@
  VERSION = 5
  PATCHLEVEL = 1
- SUBLEVEL = 8
+ SUBLEVEL = 15
 -EXTRAVERSION =
 +EXTRAVERSION = -openpower1
  NAME = Shy Crocodile