gitignore: Add more types of tags
gitignore: Add more types of tags

This covers .tags (and .tags1, etc) as made by Atom, and GTAGS, GRTAGS and
GPATH as made by GNU Global.

Signed-off-by: Russell Currey <b5ebcef270cdc73fa0593440445c07a93ae1bccb@russell.cc>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

stewart-ibm/skiboot,legoater/skiboot,mikey/skiboot,legoater/skiboot,mikey/skiboot,mikey/skiboot,shenki/skiboot,shenki/skiboot,qemu/skiboot,shenki/skiboot,legoater/skiboot,qemu/skiboot,stewart-ibm/skiboot,open-power/skiboot,qemu/skiboot,open-power/skiboot,open-power/skiboot,stewart-ibm/skiboot,qemu/skiboot,legoater/skiboot,qemu/skiboot,legoater/skiboot,open-power/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot