xtensa: tell git to ignore generated files

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/boot/.gitignore

@@ -0,0 +1,2 @@
+uImage
+zImage.redboot

arch/xtensa/boot/boot-elf/.gitignore

@@ -0,0 +1 @@
+boot.lds

arch/xtensa/kernel/.gitignore

@@ -0,0 +1 @@
+vmlinux.lds