Fix pre-processor defs parsing with recursive includes

[GitHub pull_request - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-utils pull request #140 was opened from ranj063:

Since the Define {} config has been removed form the input_cfg, use the
tplg_pp->define_cfg_merged for search for variable definitions. Also,
fix the parsing logic to first merge all variables from the conf files
recursively and then override them with the command line definitions.

Request URL   : https://github.com/alsa-project/alsa-utils/pull/140
Patch URL     : https://github.com/alsa-project/alsa-utils/pull/140.patch
Repository URL: https://github.com/alsa-project/alsa-utils