kernel: Move to Linux v4.19.26-openpower1

PowerPC fixes (v4.19.14 through to v4.19.26):

 powerpc/radix: Fix kernel crash with mremap()
 powerpc/fadump: Do not allow hot-remove memory from fadump reserved area.
 powerpc/powernv/ioda: Allocate indirect TCE levels of cached userspace addresses on demand
 powerpc/perf: Fix thresholding counter data for unknown type
 powerpc/uaccess: fix warning/error with access_ok()
 powerpc/xmon: Fix invocation inside lock region
 powerpc/boot: Set target when cross-compiling for clang
 powerpc: Disable -Wbuiltin-requires-header when setjmp is used
 powerpc: avoid -mno-sched-epilog on GCC 4.9 and newer
 powerpc: consolidate -mno-sched-epilog into FTRACE flags
 powerpc: remove old GCC version checks
 powerpc/mm: Fallback to RAM if the altmap is unusable
 powerpc/mm: Fix linux page tables build with some configs

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/witherspoon_dev_defconfig b/openpower/configs/witherspoon_dev_defconfig
index cda370f..0d7b51d 100644
--- a/openpower/configs/witherspoon_dev_defconfig
+++ b/openpower/configs/witherspoon_dev_defconfig
@@ -17,7 +17,7 @@
 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="4.19.13"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.19.26"
 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"