panfrost: Make {midgard,bifrost}_compile_shader_nir() return a program object

panfrost: Make {midgard,bifrost}_compile_shader_nir() return a program object

Letting the caller zero-initialize the program object is error prone,
not to mention that resources attached to the program might not be freed
by the caller. Let's simplify that by letting the compiler allocate the
panfrost_program object. Those objects should be freed with ralloc_free().

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7206>