drm: Rename reserve/unreserve to lock/unlock in GEM VRAM helpers

To align with the rest of DRM terminology, the GEM VRAM helpers now use
lock and unlock in places where reserve and unreserve where used before.
All callers have been adapted.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20190521110831.20200-3-tzimmermann@suse.de


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>