pinctrl: renesas: sh7724: Optimize fixed-width reserved fields

Describe registers with fixed-width register fields and many reserved
fields using the PINMUX_CFG_REG_VAR() macro, as the latter supports a
shorthand not requiring dummy values.

This reduces kernel size by 8 bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/696dcad42a8b8395276301eb5dd5c5a895826f35.1649865241.git.geert+renesas@glider.be

drivers/pinctrl/renesas/pfc-sh7724.c

@@ -1798,9 +1798,10 @@ static const struct pinmux_cfg_reg pinmux_config_regs[] = {
 		PTF1_FN, PTF1_OUT, 0, PTF1_IN,
 		PTF0_FN, PTF0_OUT, 0, PTF0_IN ))
 	},
-	{ PINMUX_CFG_REG("PGCR", 0xa405010c, 16, 2, GROUP(
-		0, 0, 0, 0,
-		0, 0, 0, 0,
+	{ PINMUX_CFG_REG_VAR("PGCR", 0xa405010c, 16,
+			     GROUP(-4, 2, 2, 2, 2, 2, 2),
+			     GROUP(
+		/* RESERVED [4] */
 		PTG5_FN, PTG5_OUT, 0, 0,
 		PTG4_FN, PTG4_OUT, 0, 0,
 		PTG3_FN, PTG3_OUT, 0, 0,