mesa: add support for RustiCL under PACKAGECONFIG "opencl"

mesa: add support for RustiCL under PACKAGECONFIG "opencl"

Mesa now has two OpenCL implementations: Clover (older one) and RustiCL
(newer one). Extend the "opencl" package config to include both
implementations into the libopencl-mesa (-dev) packages. As the Clover
implementation is in maintenance mode and is expected to be removed at
Mesa 25.2, it doesn't make sense to split the packages or to provide
two config options.

Signed-off-by: Zoltán Böszörményi <zboszor@gmail.com>
[DB: merged "rusticl" and "clover" back to "opencl", reworked rust inheritance]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>