openblocks_a6_defconfig: bump to linux-4.11.5 to fix build with gcc 6

The recent change to default to gcc 6 for the internal toolchain broke this
defconfig, as the kernel doesn't contain commit cb984d101b (compiler-gcc:
integrate the various compiler-gcc[345].h files) which was added during the
4.2 cycle.

Fix the build by bumping the kernel to 4.11.5.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/openblocks_a6_defconfig

@@ -10,13 +10,13 @@ BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"
 BR2_TARGET_ROOTFS_JFFS2=y
 BR2_TARGET_ROOTFS_JFFS2_NANDFLASH_128K=y
 
-# Linux headers same as kernel, a 3.18 series
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_18=y
+# Linux headers same as kernel, a 4.11 series
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_11=y
 
 # kernel
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="3.18.1"
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.11.5"
 BR2_LINUX_KERNEL_DEFCONFIG="mvebu_v5"
 BR2_LINUX_KERNEL_APPENDED_UIMAGE=y
 BR2_LINUX_KERNEL_UIMAGE_LOADADDR="0x8000"