Use show_debug_regs as a boolean

Use show_debug_regs as a boolean

I happen to see that show_debug_regs is used as an arithmetic type,
but it should be a boolean,

  if (show_debug_regs > 1)

On the other hand, GDB RSP only allows setting it to either 0 or 1,
so it makes no sense to check whether it is greater than 1.  This
patch fixes it.

gdb/gdbserver:

2015-03-06  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c (aarch64_insert_point): Use
	show_debug_regs as a boolean.
	(aarch64_remove_point): Likewise.