The 'nv' command can add/remove multiple variables. Implement that
for the 'global' command aswell. Also with the 'nv' command the -r
option is for removal of variables, not for "set match". Looking at
the users of "global -r" the only user uses the command for removal
of variables and not for "Setting multiple variables to the same value"
as stated in the command help text. Let "global -r" remove variables
aswell.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>