optimize event register codes for LKET

[Li Guanglei]

Hi,
   I checked in some changes about the event register codes of LKET. 
The problem with the old codes is that register_sys_event() is a 
script function which make stap unable to optimize away the unused 
events register codes and global variables.

  Here is a comparison:

"stap -e 'probe addevent.* {}' -bMv" will reduce the Pass 4 time from 
136841real ms to 82107real ms, and the generated .ko size reduce from 
  4.2M to 3.8MB

And it will be more obvious, say, only a few events are traced, e.g, 
'stap -e "probe addevent.iosyscall.read.entry {}" -bMv' will reduce 
the Pass 4 time from 77616real ms to 8557real ms, and generated .ko 
size reduce from 1.6M to 585KB.

- Guanglei