mesa/st: glsl_to_tgsi move some helper classes to extra files

mesa/st: glsl_to_tgsi move some helper classes to extra files

To prepare the implementation of a temp register lifetime tracker
some of the classes are moved into seperate header/implementation
files to make them accessible from other files.

Specifically these are:

    class st_src_reg;
    class st_dst_reg;
    class glsl_to_tgsi_instruction;
    struct rename_reg_pair;

    int swizzle_for_type(const glsl_type *type, int component);

  as inline:

    bool is_resource_instruction(unsigned opcode);
    unsigned num_inst_dst_regs(const glsl_to_tgsi_instruction *op);
    unsigned num_inst_src_regs(const glsl_to_tgsi_instruction *op);

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>