meta-nuvoton: support build norootfs

default-distrovars.inc depend on ARCH_DEFAULT_KERNELIMAGETYPE
to set KERNEL_IMAGETYPE, vendor could overwrite KERNEL_IMAGETYPE
in configuration file to change kernel target build.

since static-norootfs.inc set KERNEL_IMAGETYPE and KERNEL_IMAGETYPES
as ARCH_DEFAULT_KERNELIMAGETYPE, we overwrite both value to "Image"
since arm64 kernel doesn't support zImage target.

Add FLASH_MANIFEST_OFFSET and merge_bootloader in nuvoton npcm8xx.
Add compress kernel image when build norootfs.

Tested:
build norootfs evb-npcm845 target ok
flash norootfs flash-evb-npcm845 image ok

Signed-off-by: James Chiang <cpchiang1@nuvoton.com>
Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: I688cd48f2cc43f464e23f4a1f5408ce5b7195c56
diff --git a/meta-nuvoton/conf/machine/include/npcm8xx.inc b/meta-nuvoton/conf/machine/include/npcm8xx.inc
index 24956a2..a0f347c 100644
--- a/meta-nuvoton/conf/machine/include/npcm8xx.inc
+++ b/meta-nuvoton/conf/machine/include/npcm8xx.inc
@@ -6,6 +6,10 @@
 require conf/machine/include/igps-keys.inc
 
 KERNEL_IMAGETYPE ?= "Image"
+
+KERNEL_IMAGETYPE:df-obmc-static-norootfs = "Image"
+KERNEL_IMAGETYPES:df-obmc-static-norootfs = "${KERNEL_IMAGETYPE}"
+
 KERNEL_EXTRA_ARGS ?= "UIMAGE_LOADADDR=0x00008000"
 
 UBOOT_MACHINE ?= "ArbelEVB_defconfig"