Replace breakpoint_reinsert_addr by get_next_pcs operation in GDBServer

This patch in preparation for software single step support on ARM. It refactors
breakpoint_reinsert_addr into get_next_pcs so that multiple location can be
returned.

When software single stepping there can be multiple possible next addresses
because we're stepping over a conditional branch instruction, for example.

The operation get_next_pcs handles that by returning a vector of all the
possible next addresses.

Software breakpoints are installed at each location returned.

No regressions, tested on ubuntu 14.04 ARMv7 and x86.
With gdbserver-{native,extended} / { -marm -mthumb }

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low.c (the_low_targets): Rename
	breakpoint_reinsert_addr to get_next_pcs.
	* linux-arm-low.c (the_low_targets): Likewise.
	* linux-bfin-low.c (the_low_targets): Likewise.
	* linux-cris-low.c (the_low_targets): Likewise.
	* linux-crisv32-low.c (the_low_targets): Likewise.
	* linux-low.c (can_software_single_step): Likewise.
	(install_software_single_step_breakpoints): New function.
	(start_step_over): Use install_software_single_step_breakpoints.
	* linux-low.h: New CORE_ADDR vector.
	(struct linux_target_ops) Rename breakpoint_reinsert_addr to
	get_next_pcs.
	* linux-mips-low.c (the_low_targets): Likewise.
	* linux-nios2-low.c (the_low_targets): Likewise.
	* linux-sparc-low.c (the_low_targets): Likewise.

gdb/gdbserver/linux-arm-low.c

@@ -871,7 +871,7 @@ struct linux_target_ops the_low_target = {
   arm_set_pc,
   arm_breakpoint_kind_from_pc,
   arm_sw_breakpoint_from_kind,
-  NULL, /* breakpoint_reinsert_addr */
+  NULL, /* get_next_pcs */
   0,
   arm_breakpoint_at,
   arm_supports_z_point_type,