Construct readonly regcache without address space

Construct readonly regcache without address space

The address space is useless to readonly regcache, so this patch removes
the parameter to construct readonly regcache.

address_space was added in regcache by 6c95b8d, but for read-write
regcache.  regcache::aspace is used for various breakpoint/watchpoint
checking, and these regcache are not read-only regcache.

gdb:

2017-11-02  Yao Qi  <yao.qi@linaro.org>

	* frame.c (do_frame_register_read): Remove aspace.
	* jit.c (jit_frame_sniffer): Likwise.
	* ppc-linux-tdep.c (ppu2spu_sniffer): Likewise.
	* regcache.c (regcache::regcache): Pass nullptr.
	(regcache_print): Caller updated.
	* regcache.h (regcache::regcache): Remove one constructor
	parameter aspace.