USB: Debug: make logging in debug buffer more coherent

Current event logging supports only adding debug messages to buffer,
sometimes error messages also contains useful information. Adding
error messages along with debug message in buffer will give more
clear understanding.

This change adds support for adding error logs by introducing new
macro log_event_dbg() and log_event_err(). With these logs will be
available in kernel logs and log event buffer both. Also added
another macro log_event_none() with this logs will only be added to
log_event_buffer.

Change-Id: Ia863d1657a30da382751d7e97d22c8dc90cd4f08
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>