tsc: add RDTSCP or faster variants of get_timecount()
Tested by: pho
(cherry picked from commit 9e680e4005b77e3028d28377ee3722a5260f4422)
(cherry picked from commit a013e285dfd6b89b1908ca13febb0fdb0a7f3b1f)
(cherry picked from commit 9f47eeffa3cfdcb512e2011fb00fc23c7c1a7d75)