topology: pre-process-object: Expand definitions within strings

topology: pre-process-object: Expand definitions within strings

Expand the pre-processor to allow for expanding the definitions,
object attribute references and arithmetic expressions within strings.

With this extension its possible to embedded definitions or attribute
references into topology string objects. For example:

Define {
       PCM_NUMBER	1
}

Object.Pipeline {
	pcm-playback.0 {

	Object.Widget {
		copier.1 {
			copier_type	"host"
		}
		gain.1 {
			Object.Control.mixer.1 {
				name 'hw:$[$PCM_NUMBER - 1] Playback Volume'
		}
	}

	Object.Base {
		route.1 {
			source	copier.host.$index.1
			sink	gain.$index.1
		}
	}
}

In the example the $[$PCM_NUMBER - 1] would be replaced with the
result of arithmetic expression '1 - 1' in other words '0' , and
$index in all occurrences with index attribute found from pipeline
object. Any non alpha numeric or '_' character are treated as
delimiters for variable names if $[]-notation is not used.

Fixes: https://github.com/alsa-project/alsa-utils/pull/189
Signed-off-by: Jyri Sarha <jyri.sarha@intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>