doc: [2/3] uniform the texinfo syntax for commands definition

doc: [2/3] uniform the texinfo syntax for commands definition

To avoid errors in the documentation, like the one fixed by change
http://openocd.zylin.com/6134/ , use a uniform notation across the
file so simple copy-paste will work.

Enclose every Command within curly-brackets '{...}', even single
word commands.
Patch generated through:
	sed -i 's/^\(@deffn {Command} \)\([^{][^ ]*\)/\1{\2}/' doc/openocd.texi
	sed -i 's/^\(@deffnx {Command} \)\([^{][^ ]*\)/\1{\2}/' doc/openocd.texi

Change-Id: I797e8d9f5ab0aa1936f350b340d3bdd52373f5aa
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6151
Tested-by: jenkins