panic handle: Stream call trace into emmc

panic handle: Stream call trace into emmc

BZ: 17214

Once kernel panic happened, we will save all call stack of all
threads into __log_buf and then we will write it to emmc panic
partition. With the increase of thread count, we need more
large__log_buf. It will waste more RAM buffer.

We stream the call trace from __log_buf into emmc panic
partition without allocating more RAM buffer. Once there is
some call trace logged in __log_buf, we will write all into emmc.

Change-Id: I7293c80fdadfee056694a9e1a548e2f17e955e61
Signed-off-by: Zhang Dongxing <dongxing.zhang@intel.com>
Reviewed-on: http://android.intel.com:8080/26996
Reviewed-by: Guerard, Christophe <christophe.guerard@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>