pinctrl: sh-pfc: r8a7791: Add QSPI pin groups

A QSPI function set consists of 3 groups:
  - qspi_ctrl (2 control wires)
  - qspi_data2 (2 data wires, for Single/Dual SPI)
  - qspi_data4 (4 data wires, for Quad SPI)

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>