generic: add gluon grub title

[T0biii]

change the "OpenWrt" grub title to "Gluon"

freifunkMUC/site-ffm#512

[neocturne]

Thanks! Two things to improve:

• There is a typo in your commit message ("Titel" -> "title")
• This should also be set for the armsr targets (either add it to armsr.inc as well, or use try_config in the generic target config)

[T0biii]

thanks for the review

• fixed typo
• in generic sounds good for me.
  But I wasn't quite sure where exactly I hope that fits, otherwise we can move it

[rotanid]

thanks for the review

* fixed typo

typo is still there in PR title and commit message.

[T0biii]

thanks for the review

* fixed typo

typo is still there in PR title and commit message.

crazy true, now fixed. I must have been asleep when I made the change