mm: use self-explanatory macros rather than "2"

mm: use self-explanatory macros rather than "2"

Change-Id: Ia0efe80fa2c62163b0d58a382aef1e0881cba15b
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Link: http://lkml.kernel.org/r/20200831175042.3527153-2-yuzhao@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[backport of the commit ed0173733dd468883198c3136284394320b8fad6 from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>