Use sync regs instead of get/set regs on KVM

[simongdavies]

KVM has a set of functions (sync_regs, sync_regs_mut, clear_sync_dirty_regs, clear_sync_valid_regs, set_sync_dirty_regs and set_sync_valid_regs) that cause synchronisation of registers without the need to call get/set regs, this improves performance as it means that extra ioctls are not required to retrieve or set registers.

We should replace get/set regs with the appropriate sync functions