target/cortex_m: reduce duplication in profiling

target/cortex_m: reduce duplication in profiling

The Cortex-M implementation of profiling contains a bunch of
conditionals and checks to handle both chips which have PCSR and chips
which do not. However, the net effect of the non-PCSR branches is
actually exactly the same as what target_profiling_default does. Rather
than duplicating this code, just detect the situation where PCSR isn’t
available and delegate to target_profiling_default.

Change-Id: I1be57ac77f983816ab6bf644a3cfca77b67d6f70
Signed-off-by: Christopher Head <chead@zaber.com>
Reviewed-on: http://openocd.zylin.com/5236
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>