ANDROID: mm: fix speculative walk which is unsafe under RCU

Speculative page fault handling expects MMU_GATHER_RCU_TABLE_FREE to
guarantee that page tables are stable, however tlb_remove_table() has
a slow-path fall-back case when __get_free_page() returns NULL and
tlb_remove_table_one() gets called. The way synchronization is
implemented in that function is not RCU-safe and require IRQs to be
disabled (see the comment in tlb_remove_table_sync_one()).
Fix the invalid assumption to disable IRQs even when
MMU_GATHER_RCU_TABLE_FREE=y.

Bug: 257443051
Change-Id: I227f351607cf73022cb31f6f7a232cab41cf6a5a
Signed-off-by: Suren Baghdasaryan <surenb@google.com>