Add cpu information to the info os command on linux.

Add cpu information to the info os command on linux.

This patch adds cpu information on linux based on /proc/cpuinfo as :
cpus       Listing of all cpus/cores on the system

This patch also reorders the info os commands so that they are listed
in alphabetical order.

gdb/ChangeLog:

	* NEWS: Mention info os cpus support.
	* gdb/nat/linux-osdata.c (linux_xfer_osdata_cpus): New function.
	(struct osdata_type): Add cpus entry, reorder the entries in
	alphabetical order.

gdb/doc/ChangeLog:

	* gdb.texinfo (Operating System Auxiliary Information): Add info os cpus
	documentation, reorder the info os entries in alphabetical order.