x86/p2m: Add p2m_change_type_range() operation

x86/p2m: Add p2m_change_type_range() operation
that defers the nested-p2m flush until the entire batch has been updated.
Use it in the HAP log-dirty operations for tracking VRAM changes.
This should avoid a lot of unpleasant IPI storms as the log-dirty code
on one CPU repeatedly shoots down the nested p2m of another CPU.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>