glibc: re-enable memory tagging

Now that the performance regressions caused by MTE have been resolved, we
can enable memory tagging again.

It is safe to globally enable the config as glibc does nothing if it isn't
supported on that target.

(From OE-Core rev: 5910d46b2a4b4387c12feb447c42864ec6b7828c)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>