scripts/tags.sh: Support compiled source

We usually have interst in compiled files only,
because they are strongly related to individual's work.
Current tags.sh can't select compiled files, so support it.

We can use this functionality like below.
"make cscope O=. SRCARCH=xxxx COMPILED_SOURCE=compiled"

It must be executed after building the kernel.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>