Merge "Recommend soong_config_set instead of add_soong_config_var_value"

The values of the variables can be set from a product's `BoardConfig.mk` file:

```

$(call add_soong_config_namespace, acme)

$(call add_soong_config_var_value, acme, board, soc_a)

$(call add_soong_config_var_value, acme, feature, true)

$(call add_soong_config_var_value, acme, width, 200)

$(call soong_config_set,acme,board,soc_a)

$(call soong_config_set,acme,feature,true)

$(call soong_config_set,acme,width,200)

```

The `acme_cc_defaults` module type can be used anywhere after the definition in