nls.mk: fixup cmake packages

Instead of manually overriding every cmake package that uses iconv or
gettext's paths, add the prefix in here so that at least FindIconv.cmake
works. Fixes compilation with BUILD_NLS.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

include/nls.mk

@@ -10,6 +10,7 @@ ifeq ($(CONFIG_BUILD_NLS),y)
 	INTL_PREFIX:=$(STAGING_DIR)/usr/lib/libintl-full
 	INTL_FULL:=1
 
+	CMAKE_OPTIONS += -DCMAKE_PREFIX_PATH="$(ICONV_PREFIX);$(INTL_PREFIX)"
 else
 	ICONV_PREFIX:=
 	ICONV_FULL:=