pinctrl: sh-pfc: add R8A7794 PFC support

Add PFC support for  the  R8A7794 SoC  including pin groups for some
on-chip devices such as ETH, I2C, INTC, MSIOF, QSPI, [H]SCIF...

Sergei: squashed together several patches, fixed the MLB_CLK typo,
added IRQ4.. IRQ9 pin groups, fixed IRQn comments, added ETH B pin
group names, removed stray new line and fixed typos in the  comments
in the pinmux_config_regs[] initializer, removed the platform device
ID, took into account limited number of signals in the GPIO1/5/6
controllers, added reasonable and removed unreasonable
copyrights, modified the bindings document, renamed, added changelog.

Changes in version 5:
- resolved rejects, refreshed the patch;
- added Laurent Pinchart's ACK.

Changes in version 4:
- reused the PORT_GP_26() macro to #define PORT_GP_28().

Changes in version 3:
- removed the platform device ID;
- added PORT_GP_26() and PORT_GP_28() macros, used them for GPIO1/5/6 in the
  CPU_ALL_PORT() macro.

Changes in version 2:
- rebased the patch.

Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>