kernel: Pull uImage generation into separate class

Pull the uImage image format generation from kernel.bbclass into
a separate kernel-uimage.bbclass. Introduce new KERNEL_CLASSES
variable, which allows registration of additional classes which
implement new kernel image types. The default value of is to
register kernel-uimage to preserve the original behavior.

(From OE-Core rev: 086536ac84fcc9350802c09166f600becd52a1f8)

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Koen Kooi <koen@dominion.thruhere.net>
Cc: Paul Eggleton <paul.eggleton@linux.intel.com>
Cc: Ross Burton <ross.burton@intel.com>
Cc: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/kernel-uimage.bbclass

@@ -0,0 +1,48 @@
+python __anonymous () {
+    kerneltype = d.getVar('KERNEL_IMAGETYPE', True)
+    if kerneltype == 'uImage':
+        depends = d.getVar("DEPENDS", True)
+        depends = "%s u-boot-mkimage-native" % depends
+        d.setVar("DEPENDS", depends)
+}
+
+uboot_prep_kimage() {
+	if test -e arch/${ARCH}/boot/compressed/vmlinux ; then
+		vmlinux_path="arch/${ARCH}/boot/compressed/vmlinux"
+		linux_suffix=""
+		linux_comp="none"
+	else
+		vmlinux_path="vmlinux"
+		linux_suffix=".gz"
+		linux_comp="gzip"
+	fi
+
+	${OBJCOPY} -O binary -R .note -R .comment -S "${vmlinux_path}" linux.bin
+
+	if [ "${linux_comp}" != "none" ] ; then
+		rm -f linux.bin
+		gzip -9 linux.bin
+		mv -f "linux.bin${linux_suffix}" linux.bin
+	fi
+
+	echo "${linux_comp}"
+}
+
+do_uboot_mkimage() {
+	if test "x${KERNEL_IMAGETYPE}" = "xuImage" ; then
+		if test "x${KEEPUIMAGE}" != "xyes" ; then
+			uboot_prep_kimage
+
+			ENTRYPOINT=${UBOOT_ENTRYPOINT}
+			if test -n "${UBOOT_ENTRYSYMBOL}"; then
+				ENTRYPOINT=`${HOST_PREFIX}nm ${S}/vmlinux | \
+					awk '$3=="${UBOOT_ENTRYSYMBOL}" {print $1}'`
+			fi
+
+			uboot-mkimage -A ${UBOOT_ARCH} -O linux -T kernel -C "${linux_comp}" -a ${UBOOT_LOADADDRESS} -e $ENTRYPOINT -n "${DISTRO_NAME}/${PV}/${MACHINE}" -d linux.bin arch/${ARCH}/boot/uImage
+			rm -f linux.bin
+		fi
+	fi
+}
+
+addtask uboot_mkimage before do_install after do_compile