usb: xhci_msm_hsic: Add debugfs entries to show data/ctrl events

Add two new debugfs entries to xhci-msm-hsic, "show_ctrl_events"
and "show_data_events", to allow viewing the event log buffers
from the command line. This will be useful for debugging purposes.

Change-Id: Ib5c74083eb33228ab439713861d450864f47a74c
Signed-off-by: Guang Jian Zeng <gzeng@codeaurora.org>