doc: fix texinfo warning on @deffn not at the line beginning

doc: fix texinfo warning on @deffn not at the line beginning

Commit 87a4158acf56 ("drivers: xds110: Clean up command syntax and
documentation") does not follow the documentation structure that
lists the adapters in cpt 2 "Debug Adapter Hardware" then lists
the adapter commands in cpt 8.2 "Interface Drivers"; it puts all
in cpt 2.
While doing that, uses an incorrect texinfo syntax that causes the
following warnings at compile time:
	doc/openocd.texi:543: warning: @deffn should only appear at the beginning of a line
	doc/openocd.texi:547: warning: @deffn should only appear at the beginning of a line
	doc/openocd.texi:552: warning: @deffn should only appear at the beginning of a line

Move the documentation of xds110 commands in the proper chapter
and fix the texinfo syntax.

Change-Id: I0b3f0fe0c687f194bb02e2d81aca86fcd4fdd718
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Fixes: 87a4158acf56 ("drivers: xds110: Clean up command syntax and documentation")
Reviewed-on: http://openocd.zylin.com/5613
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Edward Fewell <efewell@ti.com>