mmc: sdhci-esdhc-imx: advertise HS400 mode through MMC caps

mmc: sdhci-esdhc-imx: advertise HS400 mode through MMC caps

Instead of having an indirection through the SDHCI layer and emulating
a capability bit, that isn't there in hardware, do the same same thing
as with HS400_ES and advertise the support for HS400 directly through
the MMC caps.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Link: https://lore.kernel.org/r/20210510190400.105162-2-l.stach@pengutronix.de
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>