arm64/mm: Remove hack in mmap randomize layout

arm64/mm: Remove hack in mmap randomize layout

Since commit 4a82a99b5b4e ('random: make get_random_int() more
random'), get_random_int() returns a random value for each call,
so comment and hack introduced in mmap_rnd() as part of commit
1ca1845f7159 ('arm64: MMU fault handling and page table management')
are incorrects.

Commit 1ca1845f7159 seems to use the same hack introduced by
commit c63827563fe9 ('powerpc: Ensure random space between stack
and mmaps'), latter copied in commit 0618daed76ee ('sparc64: Sharpen
address space randomization calculations.').

But both architectures were cleaned up as part of commit
87e31da16ff0 ('powerpc+sparc64/mm: Remove hack in mmap randomize
layout') as hack is no more needed since commit 4a82a99b5b4e.

So the present patch removes the comment and the hack around
get_random_int() on AArch64's mmap_rnd().

Cc: David S. Miller <davem@davemloft.net>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Dan McGee <dpmcgee@gmail.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>