x86: Disable EXECMEM_ROX support

The whole module_writable_address() nonsense made a giant mess of
alternative.c, not to mention it still contains bugs -- notable some of the
CFI variants crash and burn.

Mike has been working on patches to clean all this up again, but given the
current state of things, this stuff just isn't ready.

Disable for now, lets try again next cycle.

Fixes: 5185e7f9 ("x86/module: enable ROX caches for module text on 64 bit")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20250113112934.GA8385@noisy.programming.kicks-ass.net