This reverts commit 399a3f0db8b0c58
"fix IRQ mode handling"
and part of commit 4a5c221f9d9bf641
"fix compability on old kernel"
MSI implementation is using irq_to_desc which is not exported before
kernel 3.4 and commit 3911ff30.
Let's revert it for release 1.7.1, waiting for another solution.
Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>