MIPS: ralink: Add rt3352 SPI_CS1 pinmux

The rt3352 has a pin that can be used as second spi chip select,
watchdog reset or GPIO. The pinmux setup was missing the definition of
said pin.

The pin is configured via the same bit on rt5350, so reuse the existing
macro.

Signed-off-by: Mathias Kresin <dev@kresin.me>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20301/
Cc: John Crispin <john@phrozen.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org