[kv2019i]

Add support for following definition for global variables:

IncludeByKey.SDW_DMIC_PCM_CHANNELS {
"1" { Define { SDW_DMIC_CHANNEL_CFG $CHANNEL_CONFIG_MONO } }
}

This doesn't currently work as the pre-processor merges the nested Define into the global define registry as a STRING value ("$CHANNEL_CONFIG_MONO"). Later, during object attribute expansion, pre_process_object_variables_expand_fcn finds the variable in the global defines and returns immediately with that unresolved string. The caller then passes "$CHANNEL_CONFIG_MONO" to the token encoder, which cannot parse it as an integer and silently substitutes 0.

Add support for double expansion for such global defines. This is similar to how local variables are already handled (see commit 0029ab7 ("topology: Expand attribute references inside $[] expressions")), and will help to reduce repeated IncludeByKey statements in topology files.

[kv2019i]

@perexg This would be useful to allow sort of definitions that are used in:
thesofproject/sof@87dc581

... we later needed to revert this as upstream alsa-utils cannot support such constructs, but upon review, I concluded this is useful facility and we should add support to upstream.

FYI @bardliao @singalsu @ujfalusi