.travis.yml: Add aarch64-* targets

Now the AArch64 targets are in mainline we can include them in our
Travis test matrix.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/.travis.yml b/.travis.yml
index 90f1676..c7ff4da 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,6 +16,7 @@
   matrix:
   - TARGETS=alpha-softmmu,alpha-linux-user
   - TARGETS=arm-softmmu,arm-linux-user
+  - TARGETS=aarch64-softmmu,aarch64-linux-user
   - TARGETS=cris-softmmu
   - TARGETS=i386-softmmu,x86_64-softmmu
   - TARGETS=lm32-softmmu