[POWERPC] Update .gitignore files

Update .gitignore as needed by dtc addition.
Signed-off-by: NJochen Friedrich <jochen@scram.de>
Acked-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/boot/.gitignore

 addnote
+dtc
 empty.c
 hack-coff
 infblock.c

arch/powerpc/boot/dtc-src/.gitignore

+dtc-lexer.lex.c
+dtc-parser.tab.c
+dtc-parser.tab.h