python/qemu: accel: Strengthen kvm_available() checks

python/qemu: accel: Strengthen kvm_available() checks

Currently kvm_available() checks for the presence of kvm module
and, if target and host arches don't mismatch. This patch adds
an 3rd checking: if QEMU binary was compiled with kvm
support.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20191216191438.93418-4-wainersm@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>