Rename mmu->sync_page to mmu->sync_spte and move the code out
of FNAME(sync_page)'s loop body into mmu.c.

No functionalities change intended.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Link: https://lore.kernel.org/r/20230216154115.710033-6-jiangshanlai@gmail.comSigned-off-by: Sean Christopherson <seanjc@google.com>