aosp.rst: use url for internal links

Use the full url rather than :ref:`page_name` for internal links to
enhance portability, i.e. be able to use the page (.rst doc) as is at a
different location, e.g. github.com, etc.

Signed-off-by: Victor Chong <victor.chong@linaro.org>

building/aosp/aosp.rst

@@ -4,7 +4,7 @@
 AOSP
 ####
 This page contains information that tells how to get OP-TEE up and running on
-HiKey devices (see :ref:`hikey`, :ref:`hikey960`) together with AOSP. The build
+HiKey devices (see `hikey`_, `hikey960`_) together with AOSP. The build
 is based on the latest OP-TEE release and updated every quarter together with
 the regular OP-TEE releases.
 
@@ -141,7 +141,7 @@ Running xtest
 Do NOT try to run ``tee-supplicant`` as it has already been started
 automatically as a service! Once booted to the command prompt, ``xtest`` can be
 run immediately from the console or an ``adb`` shell. For more details about
-running OP-TEE, please see :ref:`optee_test_run_xtest` at :ref:`optee_test`.
+running OP-TEE, please see `optee_test_run_xtest`_ at `optee_test`_.
 
 Running VTS Gtest unit for Gatekeeper and Keymaster (Optional)
 **************************************************************
@@ -185,5 +185,9 @@ Known issues
           packet in RX: status: 0x1 len: 76``) or just incompleteness of the
           generic HiKey960 builds under P.
 
+.. _hikey: https://optee.readthedocs.io/building/devices/hikey620.html#hikey
+.. _hikey960: https://optee.readthedocs.io/building/devices/hikey960.html#hikey960
 .. _official instructions: https://source.android.com/source/devices.html
 .. _Prerequisites: https://optee.readthedocs.io/building/prerequisites.html#prerequisites
+.. _optee_test_run_xtest: https://optee.readthedocs.io/building/gits/optee_test.html#optee-test-run-xtest
+.. _optee_test: https://optee.readthedocs.io/building/gits/optee_test.html#optee-test