aco_instruction_selection_setup.cpp (previously used as a header) has
been split into a header and an implementation file. The latter "only"
implements init_context and setup_isel_context, but since these files
carry a long trail of helper functions, this cleans up the isel header
a lot.
Reduces library size by 3.1% due to more functions being compiled with
static linkage. Makes aco_instruction_selection.cpp compile 3% faster.
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6504>
