selftests/nolibc: execute defconfig before other targets

selftests/nolibc: execute defconfig before other targets

Some targets use the test kernel configuration.
Executing defconfig in the same make invocation as those targets results
in errors as the configuration may be in an inconsistent state during
reconfiguration.
Avoid this by introducing ordering dependencies between the defconfig
and some other targets.

Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250123-nolibc-config-v2-4-5701c35995d6@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>