recipes: Start WORKDIR -> UNPACKDIR transition

Replace references of WORKDIR with UNPACKDIR where it makes sense to do
so in preparation for changing the default value of UNPACKDIR.

(From OE-Core rev: 1f18b9a512800860d5153d89eb82b56388efad6f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-recipe/cargo_common.bbclass

@@ -18,7 +18,7 @@
 inherit rust-common
 
 # Where we download our registry and dependencies to
-export CARGO_HOME = "${WORKDIR}/cargo_home"
+export CARGO_HOME = "${UNPACKDIR}/cargo_home"
 
 # The pkg-config-rs library used by cargo build scripts disables itself when
 # cross compiling unless this is defined. We set up pkg-config appropriately
@@ -138,7 +138,7 @@ python cargo_common_do_patch_paths() {
         return
 
     patches = dict()
-    workdir = d.getVar('WORKDIR')
+    workdir = d.getVar('UNPACKDIR')
     fetcher = bb.fetch2.Fetch(src_uri, d)
     for url in fetcher.urls:
         ud = fetcher.ud[url]