LinuxKPI; add the beginning of a tracepoint.h implementation

Add a beginning of a tracepoint.h implementation to ease porting drivers
making use of this Linux facility.

Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D34236

(cherry picked from commit a4529c46d4ee330ff6d347a611d62f4792e94392)