core: dumpvar: change info output

do not show TARGET_BUILD_APPS if it is unset

add two seperating lines, to create categories:
Build, Target, Host

Change-Id: Ib2b4e59c7c3b1e03d558d62785de1eda7fa567f8
Signed-off-by: Alexander Martinz <eviscerationls@gmail.com>