pinctrl: renesas: r8a77980: Use shorthands for reserved fields

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 168 bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/c81b26815dff2e191b8c415624a20aa3b4725d23.1649865241.git.geert+renesas@glider.be