add memory and events statistics into ktapvm

Support memory allocated/free and events hits/missed stats,
statistics is stored in percpu data.

The statistics data will report after execute script finished.

Usage:

	#./ktap -v scripts/tracepoints/eventcount.kp
	...
	[verbose] ktap stats:
	[verbose] memory allocated size: 473157
	[verbose] memory allocate num: 11039
	[verbose] memory free num: 11039
	[verbose] events_hits: 376981
	[verbose] events_missed: 0

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>