mmc: sdhci: convert sdhci_set_uhs_signaling() into a library function

Add sdhci_set_uhs_signaling() and always call the set_uhs_signaling
method.  This avoids quirks being added into sdhci_set_uhs_signaling().

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>