Handle more retcodes in eval_ccode()

Add eval_ccode() into helper

Commit adds eval_ccode() into helper in order to save some code repetition on
evaluation of retvals from _ipmi_* functions.

ID:354 - forcefully switch to C99 and more strict CFLAGS

Commit changes CFLAGS which include C99 and more strict flags. Watch out for
falling rocks.

ID:354 - uint8_t >= 0 is always true, don't test it

Commit removes test whether value is greater or equal to 0 in
is_ipmi_channel_num(), because it's always true(and it makes compiler mad).

Fix user input validation in Channel and User sub-commands

Commit fixes validation of user input in Channel and User sub-commands.

Make user User Privilege Limit is within range

Despite the fact we could leave this up to IPMI stack, we won't do that.
Therefore, is_ipmi_user_priv_limit() is added and user provided value checked.

ID:347 - Incorrect reserved channel number

Fix validation of IPMI channel numbers according to IPMIv2.0 rev1.1 and update
documentation as well.

update result ptr before return

Change-Id: If976f5c769d8ba83eefa1693e6969ef17f357ba8
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.xx.bhuvaragan@ericsson.com>

Move all files one level up in the file hierarcy, to avoid the useless ipmitool directory.