topology: pre-process-object: add support for prepocessing child objects

topology: pre-process-object: add support for prepocessing child objects

Add support for processing object instances embedded
within objects and classes. For example:
		Object.Control.mixer."0" {
			#Channel register and shift for Front Left/Right
			Object.Base.channel."fl" {
				shift	0
			}
			Object.Base.channel."fr" {
			}

			Object.Base.tlv."vtlv_m64s2" {
				Object.Base.scale."m64s2" {
					mute	1
				}
			}

			Object.Base.ops."ctl" {
				info 	"volsw"
				#256 binds the mixer control to volume get/put handlers
				get 	256
				put 	256
			}
		}

and pga class embeds the mixer objects as follows:
Class.Widget."pga" {
...
Object.Control {
		mixer."0" {...}
		mixer."1" {...}
}

The pre-processor starts with the top-pevel PGA widget object
and processes the mixer objects in the class definition.
This will recursively pre-processes its child objects to add the channels,
tlv and ops.

Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>