tools: Add additional SYM_*() stubs to linkage.h

Similar to commit f8d92fc5 ("selftests: vDSO: fix include order in
build of test_vdso_chacha") add SYM_DATA_START, SYM_DATA_START_LOCAL, and
SYM_DATA_END stubs to tools/include/linux/linkage.h so that the proper
macros can be used within the kernel's vdso code as well as in the
vdso_test_chacha selftest.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>