tests: Organize the test code to make it modular

The unit test code for libpldmresponder, host-bmc and common is
in a shared test directory. This patch separates the test code
to the respective directory.

Tested: Ran the unit test and tests passed.

Signed-off-by: Tom Joseph <rushtotom@gmail.com>
Change-Id: I31d53681fa6c0d8bc6eb7c4e3341aaff4bc341ee
diff --git a/libpldmresponder/meson.build b/libpldmresponder/meson.build
index 7e52c3d..8436e14 100644
--- a/libpldmresponder/meson.build
+++ b/libpldmresponder/meson.build
@@ -52,3 +52,7 @@
 
 libpldmresponder = declare_dependency(
   link_with: libpldmresponder)
+
+if get_option('tests').enabled()
+  subdir('test')
+endif