LICENCE: tidy up remaining GPLv2 tags and clarify ASN.1 fair use

After the licence switch to LGPL2.1 there were still some stray GPLv2
tags in the code, so swap these for SPDX tags identifying the chosen
LGPL licence.

Additionally, since the key format needs to be standardised, clarify
that the ASN.1 code defining the key format may be copied under fair
use criteria.

Reported-by: Fredrik Ternerot <fredrik.trot@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
6 files changed