UPSTREAM: arm64: compat: Reduce address limit for 64K pages

With the introduction of the config option that allows to enable kuser
helpers, it is now possible to reduce TASK_SIZE_32 when these are
disabled and 64K pages are enabled. This extends the compliance with
the section 6.5.8 of the C standard (C99).

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit 359db57c34af15edf35492944af4d4417f59886c)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398
Change-Id: I1030a5afb426470f575540811ed25929a50cfd11