drm/prime: Align gem_prime_export with obj_funcs.export

The idea is that gem_prime_export is deprecated in favor of
obj_funcs.export. That's much easier to do if both have matching
function signatures.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: "Michel Dänzer" <michel.daenzer@amd.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: Feifei Xu <Feifei.Xu@amd.com>
Cc: Jim Qu <Jim.Qu@amd.com>
Cc: Evan Quan <evan.quan@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Thomas Zimmermann <tdz@users.sourceforge.net>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Jilayne Lovejoy <opensource@jilayne.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Junwei Zhang <Jerry.Zhang@amd.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Cc: intel-gfx@lists.freedesktop.org
Cc: amd-gfx@lists.freedesktop.org
Cc: linux-tegra@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190614203615.12639-10-daniel.vetter@ffwll.ch