mmc: sdhci-of-aspeed: Add KUnit tests for phase calculations

Converting degrees of phase to logic delays is irritating to test on
hardware, so lets exercise the function using KUnit.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20210114031433.2388532-5-andrew@aj.id.au


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>