New gdbarch methods breakpoint_kind_from_pc and sw_breakpoint_from_kind
This patch adds two gdbarch methods breakpoint_kind_from_pc and
sw_breakpoint_from_kind, and uses target_info.placed_size as "kind"
of the breakpoint. This patch updates the usages of
target_info.placed_size.
The "kind" of a breakpoint is determined by gdbarch rather than
target, so we have gdbarch method breakpoint_kind_from_pc, and we
should set target_info.placed_size out of each implementation of
target to_insert_breakpoint. In this way, each target doesn't have
to set target_info.placed_size any more.
This patch also sets target_info.placed_address before
target_insert_breakpoint too, so that target to_insert_breakpoint
can use it, see record_full_insert_breakpoint.
Before we call target_insert_breakpoint, we set
target_info.placed_address and target_info.placed_size like this,