drm/tiny: drm_gem_simple_display_pipe_prepare_fb is the default

Goes through all the drivers and deletes the default hook since it's
the default now.

Acked-by: David Lechner <david@lechnology.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Emma Anholt <emma@anholt.net>
Cc: David Lechner <david@lechnology.com>
Cc: Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-aspeed@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: xen-devel@lists.xenproject.org
Link: https://patchwork.freedesktop.org/patch/msgid/20210622165511.3169559-14-daniel.vetter@ffwll.ch