zram: factor out WB and non-WB zram read functions

mainline inclusion
from mainline-v6.2-rc1
commit 5561347a
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7TWVA
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5561347aa598b6b12fb6069788ccec9b5e5ebec1

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We will use non-WB variant in ZRAM page recompression path.

Link: https://lkml.kernel.org/r/20221109115047.2921851-4-senozhatsky@chromium.org


Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Conflicts:
	drivers/block/zram/zram_drv.c

Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>