Consolidate flash image generation

Before c7248eb11c and 794bd3d4ac, flash image generation was split
between obmc-phosphor-image_types_uboot.bbclass and
image-overlay.bbclass.  This was because generate_flash() relied on
calling oe_mkimage() which was also defined in
obmc-phosphor-image_types_uboot.bbclass.  With that dependency removed,
all of the flash image generation can now be consolidated into
image-overlay.bbclass.  This location makes more sense as the .uboot
image type is for generating U-Boot legacy ramdisks while the overlay
image type is specifically for OpenBMC and its flash layout.
obmc-phopshor-image_types_uboot.bbclass is now empty and has been
removed.

Change-Id: Idcf38d3ef6f419780a7c54c77f1195bf3b5f5667
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/conf/machine/include/obmc-bsp-common.inc b/conf/machine/include/obmc-bsp-common.inc
index 99855ca..fb68f31 100644
--- a/conf/machine/include/obmc-bsp-common.inc
+++ b/conf/machine/include/obmc-bsp-common.inc
@@ -17,7 +17,7 @@
 IMAGE_FSTYPES += "cpio.${INITRAMFS_CTYPE}.u-boot"
 OBMC_IMAGE_EXTRA_INSTALL_append = " u-boot-fw-utils"
 
-IMAGE_CLASSES += "obmc-phosphor-image_types_uboot"
+IMAGE_CLASSES += "image_types_uboot"
 
 INITRAMFS_CTYPE ?= "lzma"
 INITRAMFS_FSTYPES += "cpio.${INITRAMFS_CTYPE}.u-boot"