add kernel-uimage class for fsp2

linux kernel needs u-boot tools for vmlinux post processing
in other case there will be error about:
|   BOOTAR  arch/powerpc/boot/wrapper.a
|   WRAP    arch/powerpc/boot/uImage
| INFO: Uncompressed kernel (size 0x8b7e54) overlaps the address of the wrapper(0x400000)
| INFO: Fixing the link_address of wrapper to (0x900000)
| "mkimage" command not found - U-Boot images will not be built

Change-Id: I86f4eab65c30352a1589e9e4537963f9b4a3d5fc
Signed-off-by: Ivan Mikhaylov <ivan@de.ibm.com>
diff --git a/meta-openbmc-bsp/meta-ibm/meta-fsp2/recipes-kernel/linux/linux-fsp2.inc b/meta-openbmc-bsp/meta-ibm/meta-fsp2/recipes-kernel/linux/linux-fsp2.inc
index 5b339a2..c5984b1 100644
--- a/meta-openbmc-bsp/meta-ibm/meta-fsp2/recipes-kernel/linux/linux-fsp2.inc
+++ b/meta-openbmc-bsp/meta-ibm/meta-fsp2/recipes-kernel/linux/linux-fsp2.inc
@@ -12,6 +12,7 @@
 PV = "${LINUX_VERSION}+git${SRCPV}"
 
 COMPATIBLE_MACHINE_${MACHINE} = "^${MACHINE}$"
+KERNEL_CLASSES ?= "kernel-uimage"
 
 do_patch_append() {
         for DTB in "${KERNEL_DEVICETREE}"; do