sdhci: Add new sdhci ops for platform specific tuning and delays

This patch adds new hooks for any platform specific tuning and
tap delays programing. These are needed for supporting
SD3.0.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>