x86: mm: remove architecture-specific 'access_ok()' define

There's already a generic definition of 'access_ok()' in the
asm-generic/access_ok.h header file, and the only difference bwteen that
and the x86-specific one is the added check for WARN_ON_IN_IRQ().

And it turns out that the reason for that check is long gone: it used to
use a "user_addr_max()" inline function that depended on the current
thread, and caused problems in non-thread contexts.

For details, see commits 7c478895 ("x86/uaccess, sched/preempt:
Verify access_ok() context") and in particular commit ae31fe51
("perf/x86: Restore TASK_SIZE check on frame pointer") about how and why
this came to be.

But that "current task" issue was removed in the big set_fs() removal by
Christoph Hellwig in commit 47058bb5 ("x86: remove address space
overrides using set_fs()").

So the reason for the test and the architecture-specific access_ok()
define no longer exists, and is actually harmful these days.  For
example, it led various 'copy_from_user_nmi()' games (eg using
__range_not_ok() instead, and then later converted to __access_ok() when
that became ok).

And that in turn meant that LAM was broken for the frame following
before this series, because __access_ok() used to not do the address
untagging.

Accessing user state still needs care in many contexts, but access_ok()
is not the place for this test.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>