pinctrl: renesas: sh7734: 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 174 bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/3ab96d28494b8c5a2d427ba25f31a04ca0cc7305.1649865241.git.geert+renesas@glider.be