Set kernel version to 4.2

We switch from using our own tree, to building with upstream tarballs.
Currently we still require a small number of out of tree patches; this
list will shrink as we get the last of the patches upstream, to the
point where will just set the version.

The patches are generated from the tree at
https://github.com/open-power/linux still, and imported into the
buildroot overlay.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/palmetto_defconfig b/openpower/configs/palmetto_defconfig
index 9ebb2c5..b5545ed 100644
--- a/openpower/configs/palmetto_defconfig
+++ b/openpower/configs/palmetto_defconfig
@@ -40,9 +40,9 @@
 BR2_TARGET_GENERIC_GETTY_PORT="hvc0"
 BR2_ROOTFS_OVERLAY="overlay"
 BR2_LINUX_KERNEL=y
-BR2_LINUX_KERNEL_CUSTOM_GIT=y
-BR2_LINUX_KERNEL_CUSTOM_REPO_URL="git://github.com/open-power/linux.git"
-BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="8adc30a30b88c793c2058e85426f4f94158797ad"
+BR2_LINUX_KERNEL_VERSION="4.2"
+BR2_KERNEL_HEADERS_4_2=y
+BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL)/linux"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL)/configs/linux/skiroot_defconfig"
 BR2_LINUX_KERNEL_ZIMAGE_EPAPR=y