pinctrl: renesas: r8a77990: 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 40 bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/c032fce3fff6a6a63dc90f9ab8dfe1f4f3cf6ad6.1649865241.git.geert+renesas@glider.be