mmc: sdhci: Add support for optional controller specific set_ios_post()

Some SDHCI drivers might need to do some special controller configuration
after the common clock set_ios() function has been called (speed / width
configuration). This patch adds a call to the newly created function
set_ios_port() when its configured in the host driver.

This will be used by the Xenon SDHCI controller driver used on the
Marvell Armada 3700 and 7k/8k ARM64 SoCs.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>