arm64: use hw_breakpoint_needs_single_step() to decide if step is needed

Currently we use is_default_overflow_handler() to decide whether a
"step" will be needed or not. However, is_default_overflow_handler() is
true only for perf implementation. There can be some custom kernel
module tests like samples/hw_breakpoint/data_breakpoint.c which can
rely on default step handler.

hw_breakpoint_needs_single_step() will be true if any hw_breakpoint user
wants to use default step handler and sets step_needed in hw_perf_event.

Signed-off-by: Pratyush Anand <panand@redhat.com>