Move all build and run output to out/$arch/

Most of it was present inside buildroot/output.* and the rest scattered
on top level.

This came about for the n-th time when we were reviewing QEMU trace file
locations.

On one hand, it would be cool to have per arch traces.

This made buildroot/output.${arch}~/ a natural choice.

But on the other, those traces have nothing to do with Buildroot,
and could potentially interfere with Buildroot build files.

It also feels nicer to have buildroot/ pristine source code only,
and keep all output under a single directory out/

br2

@@ -7,6 +7,12 @@ BR2_TARGET_ROOTFS_EXT2=y
 BR2_TARGET_ROOTFS_INITRAMFS=n
 BR2_TARGET_ROOTFS_EXT2_SIZE="512M"
 
+# We were tempted to do this to disable S40network neatly,
+# but that package also creates extra configuration files
+# such as /etc/network/interfaces which we need. So we just
+# remove the init.d file for now.
+#BR2_PACKAGE_IFUPDOWN_SCRIPTS=n
+
 BR2_CCACHE=y
 # Otherwise our precious debug would break!
 BR2_CCACHE_USE_BASEDIR=n
@@ -29,9 +35,6 @@ BR2_TOOLCHAIN_BUILDROOT_CXX=y
 BR2_TOOLCHAIN_BUILDROOT_FORTRAN=y
 BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
 
-# We use our own to turn it on and off at runtime.
-BR2_PACKAGE_IFUPDOWN_SCRIPTS=n
-
 # lscpu: TODO not installing?
 BR2_PACKAGE_UTIL_LINUX=y
 BR2_PACKAGE_UTIL_LINUX_BINARIES=y