esirisc: support eSi-Trace

esirisc: support eSi-Trace

This patch adds support for instruction tracing to eSi-RISC targets. The
command interface is borrowed heavily from ETM; eSi-Trace uses a less
sophisticated model for tracing, however the setup and usage is similar.
This patch also cleans up the command interfaces of the other esirisc
command groups and adds additional debugging information to log messages
when dealing with CSRs.

This patch "finalizes" support for 32-bit eSi-RISC targets.

Change-Id: Ia2a9de79a3c7c066240b5212721fb1b7584a9a45
Signed-off-by: Steven Stallion <stallion@squareup.com>
Reviewed-on: http://openocd.zylin.com/4780
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>