product_config: Set CM_BUILD priority above TARGET_BUILD_APPS

Even if we are doing TARGET_BUILD_APPS, we may want to use a cm
target for building.

Change-Id: Ic8053bc679fa8b726be90e611aeaacdf1850cabc
(cherry picked from commit d559aacd7d2b4e6dc162f3d8489a00a9bd92f23a)