Replace the full descriptions of reserved register fields by shorthands
with a negative field width, and merge adjacent reserved fields.

This reduces kernel size by 232 bytes.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1866c399e94408439a469c12dc53557b55a00f3a.1649865241.git.geert+renesas@glider.be