spi: dt-bindings: spacemit: add K3 SPI compatible

The K3 SPI controller is compatible with K1, so allow K3 device trees to
use "spacemit,k1-spi" as fallback.

Signed-off-by: Cody Kang <cody.kang.hk@outlook.com>
Signed-off-by: Zhengyu He <hezhy472013@gmail.com>
Link: https://patch.msgid.link/20260717-k3-com260-spi-v7-2-rc2-b4-preview-20260716-v1-2-969a1b0f783f@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

[ upstream commit: 6389eaf11d6cd3a66d10d0a5ea9cd91f242ccba2 ]