radeon/compute: Stop leaking LLVMContexts in radeon_llvm_parse_bitcode

radeon/compute: Stop leaking LLVMContexts in radeon_llvm_parse_bitcode

Previously we were creating a new LLVMContext every time that we called
radeon_llvm_parse_bitcode, which caused us to leak the context every time
that we compiled a CL program.

Sadly, we can't dispose of the LLVMContext at the point that it was being
created because evergreen_launch_grid (and possibly the SI equivalent) was
assuming that the context used to compile the kernels was still available.

Now, we'll create a new LLVMContext when creating EG/SI compute state, store
it there, and pass it to all of the places that need it.

The LLVM Context gets destroyed when we delete the EG/SI compute state.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
CC: "10.0" <mesa-stable@lists.freedesktop.org>