drm/vram-helper: Remove interruptible flag from public interface

The flag 'interruptible', which is passed to various functions,
is always set to be false. Remove it and hard-code the value.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200106125745.13797-7-tzimmermann@suse.de