Document new "x" and "print" memory tagging extensions

Document new "x" and "print" memory tagging extensions

Document the changes to the "print" and "x" commands to support memory
tagging.

gdb/doc/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* gdb.texinfo (Data): Document memory tagging changes to the "print"
	command.
	(Examining Memory): Document memory tagging changes to the "x"
	command.
	(Memory Tagging): Update with more information on changes to the "x"
	and "print" commands.