s390/kexec_file: add generated files to .gitignore

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/purgatory/.gitignore

@@ -0,0 +1,2 @@
+kexec-purgatory.c
+purgatory.ro