drm/arm/malidp: use drmm_* to allocate driver structures

Use drm managed resources to allocate driver structures and get rid of
the deprecated drm_dev_alloc() call and replace it with
devm_drm_dev_alloc().

This also serves as preparation to get rid of drm_device->dev_private
and to fix use-after-free issues on driver unload.

Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026155934.125294-2-dakr@redhat.com