meson: require liburing >= 0.3

openSUSE Leap 15.2 ships with liburing == 0.2 against which QEMU fails
to build.

../util/fdmon-io_uring.c: In function ‘fdmon_io_uring_need_wait’:
../util/fdmon-io_uring.c:305:9: error: implicit declaration of function ‘io_uring_sq_ready’; did you mean ‘io_uring_cq_ready’? [-Werror=implicit-function-declaration]
     if (io_uring_sq_ready(&ctx->fdmon_io_uring)) {
         ^~~~~~~~~~~~~~~~~
         io_uring_cq_ready

This method was introduced in liburing 0.3, so set that as a minimum
requirement.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20211215141949.3512719-4-berrange@redhat.com>
Message-Id: <20220105135009.1584676-4-alex.bennee@linaro.org>