drm/vc4: Move IRQ enable to PM path

drm/vc4: Move IRQ enable to PM path

We were calling enable_irq on bind, where it was already enabled previously
by the IRQ helper. Additionally, dev->irq is not set correctly until after
postinstall and so was always zero here, triggering a warning in 4.15.
Fix both by moving the enable to the power management resume path, where we
know there was a previous disable invocation during suspend.

Fixes: 5c8a7f57d7b2 ("drm/vc4: Account for interrupts in flight")
Signed-off-by: Stefan Schake <stschake@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1514563543-32511-1-git-send-email-stschake@gmail.com
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>