net: qualcomm: rmnet: Move tracepoint definitions to local file

During the initial porting process to 4.19, RmNet's tracepoints were moved
to the pre-existing trace/events/rmnet.h file. However, for backward
compatibility with older targets, they need to be moved back to the
original location.  This has the added benefit of reducing the clutter
in the trace/events directory.

Change-Id: I16678e0737a14eaf24df6162656d0ef067e27a39
Signed-off-by: Conner Huff <chuff@codeaurora.org>
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>