spi: dt-binding: add coreqspi as a fallback for mpfs-qspi

Microchip's PolarFire SoC QSPI IP core is based on coreQSPI,
so add coreqspi as a fallback to mpfs-qspi.

Signed-off-by: Naga Sureshkumar Relli <nagasuresh.relli@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220808064603.1174906-3-nagasuresh.relli@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>