gdbserver: Rename some functions, thread -> inferior

gdbserver: Rename some functions, thread -> inferior

These functions apply to thread, and not inferiors (in the gdbserver
sense, the abstraction for threads and processes, as in
inferior_list).  Therefore, it would make more sense if these functions
were named with "thread" rather than "inferior".

gdb/gdbserver/ChangeLog:

	* inferiors.h (inferior_target_data): Rename to ...
	(thread_target_data): ... this.
	(inferior_regcache_data): Rename to ...
	(thread_regcache_data): ... this.
	(set_inferior_regcache_data): Rename to ...
	(set_thread_regcache_data): ... this.
	* inferiors.c (inferior_target_data): Rename to ...
	(thread_target_data): ... this.
	(inferior_regcache_data): Rename to ...
	(thread_regcache_data): ... this.
	(set_inferior_regcache_data): Rename to ...
	(set_thread_regcache_data): ... this.
	(free_one_thread): Update.
	* linux-low.h (get_thread_lwp): Update.
	* regcache.c (get_thread_regcache): Update.
	(regcache_invalidate_thread): Update.
	(free_register_cache_thread): Update.
	* win32-i386-low.c (update_debug_registers_callback): Update.
	(win32_get_current_dr): Update.
	* win32-low.c (thread_rec): Update.
	(delete_thread_info): Update.
	(continue_one_thread): Update.
	(suspend_one_thread): Update.