entrypoints: Remove DMBs from art_quick_alloc initialized variants.

Remove the DMBs from the initialized allocation entrypoints only.
This is safe because the compiler now emits "DMB ISHST" that protects
the object for publication.

Non-initialized (resolved) entrypoints still have the "DMB ISH" because
they double as class-initialization checks, so they need to act as a
"acquire-load class status" to ensure any static field reads that follow
the new-instance or new-array would be data-race-free.

(See also b/36692143 to remove redundant barriers for class
initialization checks.)

Bug: 36656456
Bug: 36447861
Change-Id: Ie342c7e7d89febd8420cd42d8c1acf282be54c0f