arm: tegra: sdhci: Define ddr50 clock limit

Added a new variable in sdhci platform data
which will limit the ddr50 mode clock.

Bug 967719

Change-Id: I3f55b55651362447845c2e1d5000939e3e028df6
Signed-off-by: Pavan Kunapuli <pkunapuli@nvidia.com>
Reviewed-on: http://git-master/r/100569
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>
mmc: tegra: Set eMMC DDR clock based on emc clock

Set the eMMC ddr mode clock dynamically based on emc
clock rate. If ddr clock limit is specified and the emc
clock is less than max emc freq, then limit emmc ddr
clk. If not, set the max eMMC ddr clock.

Bug 967719

Change-Id: I9f70077c4ac4bb1f3e6d894fcb8420b1aba284dd
Signed-off-by: Pavan Kunapuli <pkunapuli@nvidia.com>
Reviewed-on: http://git-master/r/100579
Reviewed-by: Simone Willett <swillett@nvidia.com>
Tested-by: Simone Willett <swillett@nvidia.com>