topology: pre-process-class: add function to convert valid attribute values to intege...

topology: pre-process-class: add function to convert valid attribute values to integer tuple values

Some attributes have valid values that need to be converted
to integer tuple values before it is appended to the
object's private data:

For ex, the buffer widget object's "caps" attribute has the
following definition:
	DefineAttribute."caps" {
		type	"string"
		# Token reference and type
		token_ref	"sof_tkn_buffer.word"
		constraints {
			value_ref	"sof_tkn_mem"
			valid_values [
				"dai"
				"host"
				"pass"
				"comp"
			]
			tuple_values [
				113
				113
				113
				65
			]
		}
	}

Depending on the user input, the value string values for "caps"
will be converted to the appropriate tuple values.

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