topology: pre-process-class: Add functions to check attribute constraints

topology: pre-process-class: Add functions to check attribute constraints

Add helper functions to check if an attribute is
mandatory, immutable or unique in the class definition.
ex: for a host widget component, these are defined
as follows:

	attributes {
		#
		# host objects instantiated within the same alsaconf node must have unique
		# direction attribute
		#
		unique	"direction"
		mandatory [
			"type"
			"stream_name"
		]
		immutable [
			"uuid"
		]
	}

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