Associate target_dcache to address_space.

Associate target_dcache to address_space.

Hi,
Nowadays, 'target_dcache' is a global variable in GDB, which is not
necessary.  It can be a per-address-space variable.  In this patch, we
associate target_dcache to address_space.

gdb/doc:

2013-11-20  Yao Qi  <yao@codesourcery.com>

	* gdb.texinfo (Caching Target Data): Update doc for
	per-address-space dcache.

gdb:

2013-11-20  Yao Qi  <yao@codesourcery.com>

	* progspace.h (struct address_space_data): Declare.
	* target-dcache.c: Include "progspace.h".
	(target_dache): Remove.
	(target_dcache_aspace_key): New.
	(target_dcache_cleanup): New function.
	(target_dcache_init_p): Get data through
	target_dcache_aspace_key.
	(target_dcache_invalidate): Likewise.
	(target_dcache_get): Likewise.
	(target_dcache_get_or_init): Likewise.
	(_initialize_target_dcache): Initialize
	target_dcache_aspace_key.