obmc-phosphor-image: Variable for kernel image type written to flash

obmc-phosphor-image_types_uboot generates a complete flash image as the
last step in the build process.  This step assumed that only a single
kernel image type was being built so it used KERNEL_IMAGETYPE to
determine which kernel image to include in the flash image.  When
multiple kernel images are built via KERNEL_IMAGETYPES, a separate
variable, FLASH_KERNEL_IMAGETYPE, is needed to specify which one should
be included in the flash image. FLASH_KERNEL_IMAGETYPE has a weak
default of 'cuImage' which allows machine configs change it on a
per-machine basis.

Change-Id: I9feb327e895f15e2c289e9195a9b92dd880cded3
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/classes/obmc-phosphor-image_types_uboot.bbclass b/classes/obmc-phosphor-image_types_uboot.bbclass
index 23903d8..01f91c0 100644
--- a/classes/obmc-phosphor-image_types_uboot.bbclass
+++ b/classes/obmc-phosphor-image_types_uboot.bbclass
@@ -17,6 +17,8 @@
 FLASH_IMAGE_NAME[vardepsexclude] = "DATETIME"
 FLASH_IMAGE_LINK ?= "flash-${MACHINE}"
 
+FLASH_KERNEL_IMAGETYPE ?= "cuImage"
+
 FLASH_UBOOT_OFFSET ?= "0"
 FLASH_KERNEL_OFFSET ?= "512"
 FLASH_INITRD_OFFSET ?= "3072"
@@ -46,7 +48,7 @@
 do_generate_flash() {
        INITRD_CTYPE=${INITRAMFS_CTYPE}
        ddir="${DEPLOY_DIR_IMAGE}"
-       kernel="${KERNEL_IMAGETYPE}"
+       kernel="${FLASH_KERNEL_IMAGETYPE}"
        uboot="u-boot.${UBOOT_SUFFIX}"
        initrd="${INITRD_LINK_NAME}.cpio.${INITRD_CTYPE}"
        uinitrd="${initrd}.u-boot"