[pallas:mgpu] Deprecated using `pl.pallas_call` for Mosaic GPU kernels
The recommended API is `plgpu.kernel` with manual pipelining via
`plgpu.emit*_pipeline` if/when necessary.
I expect this change to affect almost no users, since any real world kernels
are much more likely to be using `plgpu.kernel` anyway.
PiperOrigin-RevId: 924656238