power: reset: Add support for EMMC dload

Add sysfs entry to support emmc dload mode.
Adds /sys/kernel/reset/emmc_dload entry to enable or disable
emmc dload mode support.

Change-Id: If38135427304316b03d3193ad16d335605e9c143
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>