x86/mm: Disable W^X detection and enforcement on 32-bit

The 32-bit code is in a weird spot.  Some 32-bit builds (non-PAE) do not
even have NX support.  Even PAE builds that support NX have to contend
with things like EFI data and code mixed in the same pages where W+X
is unavoidable.

The folks still running X86_32=y kernels are unlikely to care much about
NX.  That combined with the fundamental inability fix _all_ of the W+X
things means this code had little value on X86_32=y.  Disable the checks.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: linux-efi@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com/