Document the cadence qspi controller compatible for AMD Pensando
Elba SoC boards.  The Elba qspi fifo size is 1024.

Signed-off-by: Brad Larson <blarson@amd.com
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org
Link: https://lore.kernel.org/r/20230515181606.65953-3-blarson@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org