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/

trace2line

@@ -10,9 +10,9 @@ while getopts a: OPT; do
   esac
 done
 set_common_vars "$arch" false
-kernel_dir="${out_dir}/build/linux-custom"
-sed -E 's/.*pc=//' "${lkmc_out_dir}/trace.txt" | \
-  xargs "${out_dir}/host/bin/${arch}-linux-addr2line" -e "${kernel_dir}/vmlinux" -fp | \
+kernel_dir="${build_dir}/linux-custom"
+sed -E 's/.*pc=//' "${qemu_out_dir}/trace.txt" | \
+  xargs "${host_dir}/bin/${arch}-linux-addr2line" -e "${kernel_dir}/vmlinux" -fp | \
   sed -E "s|at ${kernel_dir}/(\./\|)||" | \
   uniq -c \
-> "${lkmc_out_dir}/trace-lines.txt"
+> "${qemu_out_dir}/trace-lines.txt"