Fix the issue of being unable to compile ipmi_si/ipmi_msghandler as module

The RH 6.4 tree introduced some changes to ipmi which created loop dependence
between ipmi_si and ipmi_msghandler, and in turn broke them from compiling as
modules.  However, our AliOS env are still sticking to 5u7 or 6u2 which needs
these 2 modules.

Fix it by some code moving and symbol exporting in these 2 modules.

Signed-off-by: Huang Le <le.hl@alibaba-inc.com>