tests/qtest: Make qtest_has_accel() generic

tests/qtest: Make qtest_has_accel() generic

Since commit b14a0b7469f ("accel: Use QOM classes for accel types")
accelerators are registered as QOM objects. Use QOM as a generic
API to query for available accelerators. This is in particular
useful to query hardware accelerators such HFV, Xen or WHPX which
otherwise have their definitions poisoned in "exec/poison.h".

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250130103728.536-3-philmd@linaro.org>
Signed-off-by: Fabiano Rosas <farosas@suse.de>