xen/arm: IRQ: Require desc.lock be held by callers of hw_irq_controller callbacks

xen/arm: IRQ: Require desc.lock be held by callers of hw_irq_controller callbacks

When multiple action are supported, gic_irq_{startup,shutdown} will have
to be called in the same critical section as setup/release.
Otherwise there is a race condition if at the same time CPU A is calling
release_dt_irq and CPU B is calling setup_dt_irq.

This could end up with the IRQ not being enabled.

At the same time, modify gic_irq_{enable,disable} to require desc.lock be held.

With both of theses changes, ARM's locking requirements is the same as x86's.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>