x86/mm: merge the shadow, hap and log-dirty locks into a single paging lock.

x86/mm: merge the shadow, hap and log-dirty locks into a single paging lock.

This will allow us to simplify the locking around calls between
hap/shadow and log-dirty code.  Many log-dirty paths already need the
shadow or HAP lock so it shouldn't increase contention that much.

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