arm64: NXP add LS1088a clockgen support

Add a driver for NXP LS1088a clockgen support which passes
configuration information to QorIQ clockgen class.
The implementaiton started off as copy of ls1028 support and was
adjusted accordingly.

Reviewed by: dgr_semihalf.com (earlier), mmel
MFC after: 1 week
Sponsored by: Traverse Technologies (providing Ten64 HW for testing)
Differential Revision: https://reviews.freebsd.org/D35617