Fix config loading on universal architectures
commit cef69cd4:
cerbero: Rename 'main' config to 'user' config
This is much more descriptive than 'main'.
commit a08d2f94:
cerbero: Call load_platform_config() once correctly
This reverts 5be60e8bc69725616bd54ee1d2983afb2db2469a. The mistake in
that commit was that `self._load_platform_config()` ends up not being
called at all when building for a universal platform, which causes,
f.ex., bootstrap to fail.
The new way of not calling those functions twice is clearer.
I have not tested this on native windows yet, but I will only be able to get to that on Sunday or Monday, so we should get this in to unbreak android in the meantime, f.ex., this is blocking gst-ci!224 (comment 397610).