tests/tcg: really fix path to target configuration

This was attempted in commit 533b0a1a41 ("tests/tcg: Fix target-specific
Makefile variables path for user-mode", 2022-01-12) but it also used the
wrong path; default.mak is used for config/devices, not config/targets.

While at it, explain what the inclusion is about.

Cc: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed