selftests/powerpc: Add gitignore file for the new DSCR tests

This patch adds .gitignore for all the newly added DSCR tests.
Signed-off-by: NAnshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/dscr/.gitignore

+dscr_default_test
+dscr_explicit_test
+dscr_inherit_exec_test
+dscr_inherit_test
+dscr_sysfs_test
+dscr_sysfs_thread_test
+dscr_user_test