drm/vc4: Account for interrupts in flight

Synchronously disable the IRQ to make the following cancel_work_sync
invocation effective.

An interrupt in flight could enqueue further overflow mem work. As we
free the binner BO immediately following vc4_irq_uninstall this caused
a NULL pointer dereference in the work callback vc4_overflow_mem_work.

Link: https://github.com/anholt/linux/issues/114


Signed-off-by: Stefan Schake <stschake@gmail.com>
Fixes: d5b1a78a ("drm/vc4: Add support for drawing 3D frames.")
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1510275907-993-2-git-send-email-stschake@gmail.com