spi: dt-binding: document microchip coreQSPI

Add microchip coreQSPI compatible string and update the title/description
to reflect this addition.

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/20220808064603.1174906-2-nagasuresh.relli@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>