Build: Fix issue for platform that doesn't build BL2

Problem: CMake Error on the platform that doesn't build BL2
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CMake Error at platform/ext/accelerator/CMakeLists.txt:27 (target_link_libraries):
  Cannot specify link libraries for target "platform_bl2" which is not built
  by this project.
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Solution: Move BL2 related stuff into BL2 block

Change-Id: Ifce5becde20a1c99f5369c3ae7d4357ee83bd406
Signed-off-by: Alamy Liu <alamy.liu@infineon.com>
1 file changed