drm/i915: sanitize forcewake registers on reset

drm/i915: sanitize forcewake registers on reset

In reset we try to restore the forcewake state to
pre reset state, using forcewake_count. The reset
doesn't seem to clear the forcewake bits so we
get warn on forcewake ack register not clearing.

Use same mechanism as intel_uncore_sanitize() does
when loading driver to reset the forcewake bits, right
after the chip has been reset.

Reviewed-by: Chris Wilson <[email protected]>
Signed-off-by: Mika Kuoppala <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>