drm: pl111: Fix module autoloading

Add a missing MODULE_DEVICE_TABLE entry to fix module autoloading.

Cc: Eric Anholt <eric@anholt.net>
Cc: dri-devel@lists.freedesktop.org
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200409013947.12667-2-robh@kernel.org