[aarch64-port-dev ] Freeze aarch64/jdk8

[Andrew Haley]

The jdk8 development tree at aarch64/jdk8 has been in use for some
time.  I don't think we need it any more.  aarch64/jdk8u tracks
upstream jdk8u far more closely: it differs from upstream only in the
minimum number of places needed to get AArch64 to work.

I'm proposing to close aarch64/jdk8 to all updates.  aarch64/jdk8u
will be used for all commits. jdk8 is interesting from a historical
point of view, so it will be made read only.

The rules for committing to aarch64/jdk8u are:

1.  All non-AArch64-specific patches come from jdk8u.  If you want to
change anything non-AArch64 submit it to jdk8u.

2.  All AArch64-specific patches, if they are relevant to jdk9, must
be submitted there first and back-ported to jdk8u.

Andrew.