i.MX for 2020.07

- imxrt: fix LCD clock, fix doc
- new board: Coral Dev
- imx8: enable Cache in SPL. SNVS, update SCFW API
- imx8MM: fix reset, 8MQ quand and QuadLite, CPU speed grading
- MX6ULL : is_imx6ull to include i.MX6ULZ
- Net: add config to enable TXC delay

Travis: https://travis-ci.org/github/sbabic/u-boot-imx/builds/682033914
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