yocto: fix missing file warnings

Summary:
Older versions of Yocto gave a warning when there were files
specified in the SRC_URI that were not present.  Newer versions
of Yocto prohibit this and fail in the parsing stage.  Fix these
up by ensuring the files are always present.

- mterm: only used on openbmc-fb systems, so use an OVERRIDE.
- mac-util: leverage OVERRIDE-based file searching instead of MACHINE
  in the SRC_URI.

Test Plan: Built clearcreek (dunfell) and bletchley (master)

Reviewed By: amithash

fbshipit-source-id: 77b854fcc3ea81b7d47d21d54307c3d61dda75da

common/recipes-core/mTerm/mterm_0.1.bb

@@ -34,6 +34,9 @@ LOCAL_URI = " \
     file://Makefile \
     file://mTerm/run \
     file://mTerm-service-setup.sh \
+    "
+
+LOCAL_URI:append:openbmc-fb = " \
     ${@bb.utils.contains('DISTRO_FEATURES', 'systemd', \
                          'file://mTerm_server.service', '', d)} \
     "

meta-aspeed/recipes-bsp/u-boot/files/openbmc-fb/README

@@ -0,0 +1,5 @@
+Yocto requires all files in SRC_URIs to be present, even if the recipe isn't
+explicitly used.  Inside the upstream meta/ layer there are often newer U-boot
+versions, which pick up our include files due to the same names, which causes
+them to look for `file://u-boot-${PN}` SRC_URIs.  Create empty directories
+of the correct versions to satisfy this requirement.

meta-aspeed/recipes-kernel/linux/files/defconfig-5.0/ast2620/defconfig

@@ -0,0 +1,2 @@
+# AST2620 doesn't work on kernel 5.0, but Yocto now requires all files in
+# SRC_URIs to be found.  Add an empty one just to make Yocto happy.

meta-facebook/recipes-utils/mac-util/files/eeprom.h

@@ -0,0 +1 @@
+#error Missing machine eeprom file

meta-facebook/recipes-utils/mac-util/mac-util_0.1.bb

@@ -9,7 +9,7 @@ LIC_FILES_CHKSUM = "file://mac-util.cpp;beginline=4;endline=16;md5=94a0865391a64
 LOCAL_URI += " \
     file://mac-util.cpp \
     file://Makefile \
-    file://${MACHINE}/eeprom.h \
+    file://eeprom.h \
     "
 CXXFLAGS:prepend:${MACHINE} = "-I${MACHINE} "
 LDFLAGS += "-lobmc-i2c"