pinctrl: ingenic: Fix JZ4760 support

- JZ4760 and JZ4760B have a similar register layout as the JZ4740, and
  don't use the new register layout, which was introduced with the
  JZ4770 SoC and not the JZ4760 or JZ4760B SoCs.

- The JZ4740 code path only expected two function modes to be
  configurable for each pin, and wouldn't work with more than two. Fix
  it for the JZ4760, which has four configurable function modes.

Fixes: 0257595a

 ("pinctrl: Ingenic: Add pinctrl driver for JZ4760 and JZ4760B.")
Cc: <stable@vger.kernel.org> # 5.3
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20201211232810.261565-1-paul@crapouillou.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>