int -> enum target_hw_bp_type in aarch64-linux-nat.c

int -> enum target_hw_bp_type in aarch64-linux-nat.c

This patch is to use 'enum target_hw_bp_type' instead of int for
breakpoint type, in order to make some functions in GDB and
GDBserver looks similar.

gdb:

2015-07-17  Yao Qi  <yao.qi@linaro.org>

	* aarch64-linux-nat.c (aarch64_dr_state_insert_one_point): Change
	argument type's type to 'enum target_hw_bp_type'.
	(aarch64_dr_state_remove_one_point): Likewise.
	(aarch64_handle_breakpoint): Likewise.
	(aarch64_linux_insert_hw_breakpoint): Likewise.
	(aarch64_linux_remove_hw_breakpoint): Likewise.
	(aarch64_handle_aligned_watchpoint): Likewise.