target/i386: emulate: add new callbacks

On Hyper-V fetching some guest registers is really expensive, so
add a way to query some state from information provided by Hyper-V
to save time on vmexits.

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
Link: https://lore.kernel.org/r/20260324151323.74473-7-mohamed@unpredictable.fr
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>