dt-bindings: spi: convert spi-brcm63xx.txt to YAML

Changes done during conversion:

* added a description, lifting and adapting the limitation sentence from
brcm,bcm63xx-hsspi.yml
* added appropriate compatibles for all SoCs that are supported by
bcm63xx/bmips

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://lore.kernel.org/r/20230727070806.12205-1-jonas.gorski@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>