drm/ssd130x: Allocate buffer in the plane's .atomic_check() callback

Drivers are not allowed to fail after drm_atomic_helper_swap_state() has
been called and the new atomic state is stored into the current sw state.

Since the struct ssd130x_device .data_array is allocated in the encoder's
.atomic_enable callback, the operation can fail and this is after the new
state has been stored. So it can break an atomic mode settings assumption.

Fix this by having custom helpers to allocate, duplicate and destroy the
plane state, that will take care of allocating and freeing these buffers.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230726105433.389740-2-javierm@redhat.com