hw/tricore: fix inclusion of tricore_testboard

hw/tricore: fix inclusion of tricore_testboard

Because commit f4063f9c319e39 ("meson: Introduce target-specific
Kconfig") ended being merged after commit 582079c9d27fc8cfff9f49
("hw/tricore: Add testdevice for tests in tests/tcg/"), we
inadvertently added a symbol clash causing the build not to include
the testboard needed for check-tcg.

Fixes: f4063f9c31 ("meson: Introduce target-specific Kconfig")
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210720114057.32053-2-alex.bennee@linaro.org>
[PMD: Updated description mentioning commits merged]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>