mmc: sdhci: cache timing information locally

mmc: sdhci: cache timing information locally

Rather than reading back the timing information from the registers,
cache it locally.  This allows implementations to translate the UHS
timing by overriding the set_uhs_signaling() method as required
without also having to emulate the SDHCI_HOST_CONTROL2 register.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
[Ulf Hansson] Resolved conflict
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>