remote: remote_arch_state pointers -> remote_arch_state objects

remote: remote_arch_state pointers -> remote_arch_state objects

The previous patch made the map store pointers to remote_arch_state
instead of objects directly, simply because struct remote_arch_state
is still incomplete where struct remote_state is declared.  This patch
thus moves the remote_arch_state declaration higher up in the file,
and makes the map store remote_arch_state objects directly instead of
pointers to objects.

gdb/ChangeLog:
2018-05-22  Pedro Alves  <palves@redhat.com>

	* remote.c (struct packet_reg, struct remote_arch_state):
	Move higher up in the file.
	(remote_state) <m_arch_states>: Store remote_arch_state values
	instead of remote_arch_state pointers.
	(remote_state::get_remote_arch_state): Adjust.