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 769 bytes.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/616afe67d3b4d2cbf5f43876f9aa7b258862ceaa.1649865241.git.geert+renesas@glider.be