arm64: mops: Document requirements for hypervisors

Add a mops.rst document to clarify in more detail what hypervisors need
to do to run a Linux guest on a system with FEAT_MOPS.

Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Link: https://lore.kernel.org/r/20241028185721.52852-1-kristina.martsenko@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>