gdb: rename gdbarch_software_single_step -> gdbarch_get_next_pcs

I spotted this while reviewing a patch adding a new
gdbarch_software_single_step implementation.  I find the name
"software_single_step" a bit misleading or unclear.  It makes it sounds
as if the function executed a single step.  In reality, this function
returns the possible next PCs for current instructions.

We have a similar concept in GDBserver:
linux_process_target::low_get_next_pcs.  I like that name, it's clear
and straight to the point.

Rename gdbarch_software_single_step to gdbarch_get_next_pcs.  I find
this name more indicative of what happens.

There is some code for ARM shared between GDB and GDBserver to implement
both sides, also called "get next pcs", so I think it all fits well
together.

Tested by rebuilding.

Change-Id: Ide74011a5034ba11117b7e7c865a093ef0b1dece
Approved-by: Kevin Buettner <kevinb@redhat.com>
Acked-by: Luis Machado <luis.machado.foss@gmail.com>

gdb/gdbarch_components.py

@@ -1395,7 +1395,7 @@ the condition is true, so that we ensure forward progress when stepping
 past a conditional branch to self.
 """,
     type="std::vector<CORE_ADDR>",
-    name="software_single_step",
+    name="get_next_pcs",
     params=[("struct regcache *", "regcache")],
     predicate=True,
 )
@@ -1891,7 +1891,7 @@ receive control again (e.g. by placing a software breakpoint instruction into
 the displaced instruction buffer).
 
 The default implementation returns false on all targets that provide a
-gdbarch_software_single_step routine, and true otherwise.
+gdbarch_get_next_pcs routine, and true otherwise.
 """,
     type="bool",
     name="displaced_step_hw_singlestep",