Add qga/qapi-generated to .gitignore

The folder "qga/qapi-generated" shows up after building QEMU, and
gets in the way during e.g. "git add ."; Add it to .gitignore to
keep it from accidentally ending up in the wrong place.
Signed-off-by: NGabriel Somlo <somlo@cmu.edu>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

.gitignore

@@ -21,6 +21,7 @@
 libdis*
 libuser
 /linux-headers/asm
+/qga/qapi-generated
 /qapi-generated
 /qapi-types.[ch]
 /qapi-visit.[ch]