meta: fix unpack warnings from recipes with only in-tree files

There is now a check that ${S} exists after running do_unpack.
The convention for recipes with only local in-tree files is
to define S and point UNPACKDIR at the same directory.  All
such recipes are updated to use this convention.

Signed-off-by: Matt Madison <matt@madison.systems>

recipes-core/initrdscripts/tegra-flash-init_1.0.bb

@@ -9,6 +9,9 @@ SRC_URI = "\
     file://initrd-flash.scheme.in \
 "
 
+S = "${WORKDIR}/sources"
+UNPACKDIR = "${S}"
+
 COMPATIBLE_MACHINE = "(tegra)"
 
 do_install() {

recipes-core/initrdscripts/tegra-minimal-init_1.0.bb

@@ -7,6 +7,9 @@ SRC_URI = "\
     file://platform-preboot.sh \
 "
 
+S = "${WORKDIR}/sources"
+UNPACKDIR = "${S}"
+
 COMPATIBLE_MACHINE = "(tegra)"
 
 PACKAGE_ARCH = "${MACHINE_ARCH}"