sdk: add spidev-test to the bundle of userspace sources

moves and extends the current facilities, which have been
added some time ago for the the usbip utility, to support
more utilites that are shipped with the Linux kernel tree
to the SDK.

this allows to drop all the hand-waving and code for
failed previous attempts to mitigate the SDK build failures.

Fixes: bdaaf66e28 ("utils/spidev_test: build package directly from Linux")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

package/utils/spidev_test/Makefile

@@ -10,7 +10,6 @@ include $(INCLUDE_DIR)/kernel.mk
 
 PKG_NAME:=spidev-test
 PKG_RELEASE:=$(LINUX_VERSION)
-PKG_FLAGS:=nonshared
 PKG_BUILD_DIR:=$(LINUX_DIR)/tools/spi-$(TARGET_DIR_NAME)
 PKG_BUILD_PARALLEL:=1
 
@@ -19,7 +18,7 @@ include $(INCLUDE_DIR)/package.mk
 define Package/spidev-test
   SECTION:=utils
   CATEGORY:=Utilities
-  DEPENDS:=+PACKAGE_kmod-spi-dev:kmod-spi-dev @!IN_SDK
+  DEPENDS:=+kmod-spi-dev
   TITLE:=SPI testing utility
   VERSION:=$(LINUX_VERSION)-$(PKG_RELEASE)
   URL:=http://www.kernel.org
@@ -30,6 +29,8 @@ define Package/spidev-test/description
 endef
 
 define Build/Prepare
+	# For SDK: Sources are copied by target/sdk/Makefile's
+	# USERSPACE_UTILS(_FILES)
 	$(CP) $(LINUX_DIR)/tools/spi/* $(PKG_BUILD_DIR)/
 endef