imx-test: Fix linking failures of test utilities

imx-test: Fix linking failures of test utilities

Some of the unit-tests were not being built due to differences on how
the build system behaves when running inside of the OE-Core. This
fixes those minor issues and increases the number of tests available.

This increases the number of tests which build successfully.

The new built tests, when building for i.MX6Q are:

,----
| /unit_tests/hciattach-ar3k.bin
| /unit_tests/config_dec
| /unit_tests/akiyo.mp4
| /unit_tests/config_net
| /unit_tests/mxc_vpu_test.out
| /unit_tests/config_encdec
| /unit_tests/autorun-vpu.sh
| /unit_tests/memtool
| /unit_tests/config_enc
`----

When building for i.MX53 those are:

,----
| /unit_tests/hciattach-ar3k.bin
| /unit_tests/memtool
`----

And when building for i.MX28 those are:

,----
| /unit_tests/mxc_pf_test.out
| /unit_tests/mmdc2
| /unit_tests/key_slot_tests.sh
| /unit_tests/mxc_isl29023.out
| /unit_tests/partition_tests.sh
| /unit_tests/fail_mode_tests.sh
| /unit_tests/scc_test
| /unit_tests/scc2_setup.sh
| /unit_tests/autorun-scc2.sh
| /unit_tests/autorun-scc.sh
| /unit_tests/encrypt_decrypt_tests.sh
| /unit_tests/mxc_fb_test.out
| /unit_tests/memtool
| /unit_tests/scc2_test.out
| /unit_tests/autorun.sh
| /unit_tests/mxc_mlb_test.out
| /unit_tests/scc_setup.sh
| /unit_tests/test_subs.sh
| /unit_tests/all-suite.txt
`----

Change-Id: I58882adc22990d9ec53dc9ead034e85acd64375e
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>