mhi: core: expose soc reset and register dump debugfs entries

For debug purposes, allow clients to issue SOC reset or read the entire
register dump when they wish to do so. They may not read proper values
or the reset may not take effect if the device is powered down.

Change-Id: I7fb7589a1bdfd5d7c610bdf6aab5edfc814cdceb
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>