Changes to the x86 entry code in v6.7:

 - Make IA32_EMULATION boot time configurable with
   the new ia32_emulation=<bool> boot option.

 - Clean up fast syscall return validation code: convert
   it to C and refactor the code.

 - As part of this, optimize the canonical RIP test code.

Signed-off-by: Ingo Molnar <mingo@kernel.org>