.gitignore: Add .dtbo and .itb files to top level list

Compiled overlay related blobs shouldn't be committed in the kernel
tree, so ignore these for git.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

.gitignore

@@ -17,11 +17,13 @@
 *.c.[012]*.*
 *.dtb
 *.dtb.S
+*.dtbo
 *.dwo
 *.elf
 *.gcno
 *.gz
 *.i
+*.itb
 *.ko
 *.lex.c
 *.ll