firmware: xilinx: Add DLL reset support

SD DLL resets are required for some of the operations on ZynqMP platform.
Add DLL reset support in ZynqMP firmware driver for SD DLL reset.

Signed-off-by: Manish Narani <manish.narani@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/1579602095-30060-3-git-send-email-manish.narani@xilinx.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>