Move trusted firmware repo to new location

Transition to the new trusted firmware repo location at
http://git.trustedfirmware.org

.

NOTE: The 'arm-trusted-firmware' instances under zynqmp* have not
been changed.

Signed-off-by: Victor Chong <victor.chong@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>