remote_target::m_remote_state, pointer -> object

remote_target::m_remote_state, pointer -> object

The only reason remote_target::m_remote_state is a pointer is that
struct remote_state is incomplete when struct remote_target is
defined.

This commit thus moves struct remote_state (and its dependencies)
higher up and makes remote_target::m_remote_state an object instead of
a pointer.

gdb/ChangeLog:
2018-05-25  Pedro Alves  <palves@redhat.com>

	* remote.c (struct vCont_action_support, MAXTHREADLISTRESULTS)
	(struct readahead_cache, struct packet_reg, struct
	remote_arch_state, class remote_state): Move higher up in the
	file.
	(remote_target::m_remote_state): Now an object instead of a pointer.
	(remote_target::get_remote_state): Adjust.