sdhci: add i.MX SD Stable Clock bit

Add the ESDHC PRSSTAT_SDSTB bit, using the value of SDHC_CLOCK_INT_STABLE.
Freescale recommends checking this bit when changing clock frequency.

Signed-off-by: Hans-Erik Floryd <hans-erik.floryd@rt-labs.com>
Message-id: 1534507843-4251-1-git-send-email-hans-erik.floryd@rt-labs.com
[PMM: fixed indentation]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2 files changed