topology: pre-processor: support to include conf block with IncludeByKey

topology: pre-processor: support to include conf block with IncludeByKey

Currently, The IncludeByKey mechanism only supports conditionally
including a topology conf file. Even if we only
want to conditionally include a small conf block, we have
to use a conf file and in the end we will have a lot of
trivial conf files that only contain a single conf blocks.

This patch extends the use of IncludeByKey ito support including conf
blocks conditionally. For example, the block below will include the route
conditionally based on the variable definition COPIER_ROUTE.

Define {
	COPIER_ROUTE	1
}

IncludeByKey.COPIER_ROUTE {
       	"1" {
		Object.Base.route.11 {
			source	copier.module.8.2
			sink	copier.module.17.2
		}
	    }
}

Fixes: https://github.com/alsa-project/alsa-utils/pull/187
Signed-off-by: Chao Song <chao.song@linux.intel.com>
Co-authored-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>