spi: Add DT bindings documentation for Netlogic XLP SPI controller

Add DT bindings documentation for SPI controller driver used by
Netlogic XLP MIPS64 SoCs.

Signed-off-by: Kamlakant Patel <kamlakant.patel@broadcom.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed