Several small readability improvements:
- Move enum gate_type definition up and add comments to each field.
- Use this enum instead of generic uint32_t type in clock desc struct.
- Tidy up bitfield syntax and comments in clock desc structure
- Reformat macros for building clock desc to have one assignment per line

There is no functional change.
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230301215520.828455-2-ralph.siemsen@linaro.orgSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>