SlowPath: Remove the use of Locations in the SlowPath constructors.

The main motivation is that using locations in the SlowPath constructors
ties us to creating the SlowPaths after register allocation, since before
the locations are invalid.

A later patch of the series will be moving the SlowPath creation to the
LocationsBuilder visitors. This will enable us to add more checking as
well as consider sharing multiple SlowPaths of the same type.

Change-Id: I7e96dcc2b5586d15153c942373e9281ecfe013f0
Signed-off-by: Serban Constantinescu <serban.constantinescu@linaro.org>