add support for no Linux kernel builds, use it for arcturus-ucbf54x

mk/build.mk

@@ -179,9 +179,13 @@ ifeq ($(ADK_TARGET_OS_BAREMETAL),y)
 	$(MAKE) -f mk/build.mk package/hostcompile toolchain/final
 endif
 ifeq ($(ADK_TARGET_OS_LINUX),y)
+ifeq ($(ADK_TARGET_NO_KERNEL),y)
+	$(MAKE) -f mk/build.mk package/hostcompile toolchain/final package_clean package/compile root_clean package/install package_index
+else
 	$(MAKE) -f mk/build.mk package/hostcompile toolchain/final target/config-prepare target/compile package_clean package/compile root_clean package/install target/install package_index
 endif
 endif
+endif
 
 package_index:
 ifeq ($(ADK_TARGET_PACKAGE_IPKG),y)

package/busybox/config/coreutils/Config.in

@@ -719,12 +719,12 @@ config BUSYBOX_SUM
 	checksum and count the blocks in a file
 config BUSYBOX_SYNC
 	bool "sync (3.8 kb)"
-	default y
+	default n
 	help
 	sync is used to flush filesystem buffers.
 config BUSYBOX_FEATURE_SYNC_FANCY
 	bool "Enable -d and -f flags (requires syncfs(2) in libc)"
-	default y
+	default n
 	depends on BUSYBOX_SYNC
 	help
 	sync -d FILE... executes fdatasync() on each FILE.

package/busybox/config/util-linux/Config.in

@@ -660,7 +660,7 @@ config BUSYBOX_NOLOGIN_DEPENDENCIES
 	disable this option.
 config BUSYBOX_NSENTER
 	bool "nsenter (6.5 kb)"
-	default y
+	default n
 	help
 	Run program with namespaces of other processes.
 config BUSYBOX_PIVOT_ROOT

target/bfin/systems/arcturus-ucbf54x

@@ -3,8 +3,7 @@ config ADK_TARGET_SYSTEM_ARCTURUS_UCBF54X
 	select ADK_TARGET_CPU_BFIN_BF548
 	select ADK_TARGET_WITH_NETDEVICE
 	select ADK_TARGET_WITH_SERIAL
-	select ADK_TARGET_KERNEL_WITH_COMPRESSION
-	select ADK_TARGET_KERNEL_IMAGE_GZ
+	select ADK_TARGET_NO_KERNEL
 	select ADK_TARGET_PACKAGE_TXZ
 	help
 	  Arcturus uCBF54x.

target/config/Config.in.kernelfmt

@@ -77,6 +77,9 @@ config ADK_TARGET_KERNEL
 	default "bzImage" if ADK_TARGET_SYSTEM_GENERIC_X86_64 || ADK_TARGET_SYSTEM_GENERIC_X86
 	default "vmlinux"
 
+config ADK_TARGET_NO_KERNEL
+	bool
+
 config ADK_TARGET_KERNEL_WITH_COMPRESSION
 	bool