linux: Update to v4.2.1-openpower1

This brings in the 4.2.1 stable release, and the accraid RAID driver for
PMC-Sierra RAID  on Habanero.

The RAID driver is submitted upstream to the linux-scsi mailing list,
but is not yet in a tree.

The stable release brings in a few commits that are of interest to
OpenPower platforms:

 94d718d024e xfs: return errors from partial I/O failures to files
 2937b784b19 xfs: Fix file type directory corruption for btree directories
 95310b79776 libxfs: readahead of dir3 data blocks should use the read verifier
 0a3b19cef4f sched: Fix cpu_active_mask/cpu_online_mask race

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/firestone_defconfig b/openpower/configs/firestone_defconfig
index 99cc70d..10835f2 100644
--- a/openpower/configs/firestone_defconfig
+++ b/openpower/configs/firestone_defconfig
@@ -43,7 +43,7 @@
 BR2_ROOTFS_DEVICE_TABLE="../openpower/device_table.txt"
 BR2_ROOTFS_POST_BUILD_SCRIPT="../openpower/scripts/fixup-target-var"
 BR2_LINUX_KERNEL=y
-BR2_LINUX_KERNEL_VERSION="4.2"
+BR2_LINUX_KERNEL_VERSION="4.2.1"
 BR2_KERNEL_HEADERS_4_2=y
 BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL)/linux"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y