multiconfig: Enable multiconfig dependencies on oe-core

This patch enables multiconfig dependencies (mcdepends) to be used on
recipes using the following format:

task[mcdepends] = "multiconfig:FROM-MC:TO-MC:PN:task-to-depend-on"

For the sake of simplicity consider the following example:

Assuming we have set up multiconfig builds, one for qemux86 and one for
qemuarm, named x86 and arm respectively.

Adding the following line to an image recipe (core-image-sato):
do_image[mcdepends] = "multiconfig:x86:arm:core-image-minimal:do_rootfs"

Would state that core-image-sato:do_image from x86 will depend on
core-image-minimal:do_rootfs from arm so it can be executed.

This patch makes modifications to bitbake.conf to enable mcdepends, and
to sstatesig and staging.bbclass to avoid conflicts between packages from
different multiconfigs.

[YOCTO #10681]

(From OE-Core rev: f71bfe833c657244d2fd07b3b71e86081d7d1c04)

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandr@xilinx.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/staging.bbclass

@@ -256,7 +256,7 @@ python extend_recipe_sysroot() {
     workdir = d.getVar("WORKDIR")
     #bb.warn(str(taskdepdata))
     pn = d.getVar("PN")
-
+    mc = d.getVar("BB_CURRENT_MC")
     stagingdir = d.getVar("STAGING_DIR")
     sharedmanifests = d.getVar("COMPONENTS_DIR") + "/manifests"
     recipesysroot = d.getVar("RECIPE_SYSROOT")
@@ -443,7 +443,13 @@ python extend_recipe_sysroot() {
 
     msg_exists = []
     msg_adding = []
+
     for dep in configuredeps:
+        if mc != 'default':
+            # We should not care about other multiconfigs
+            depmc = dep.split(':')[1]
+            if depmc != mc:
+                continue
         c = setscenedeps[dep][0]
         if c not in installed:
             continue