x86/Kconfig: only enable ROX cache in execmem when STRICT_MODULE_RWX is set

Currently ROX cache in execmem is enabled regardless of
STRICT_MODULE_RWX setting. This breaks an assumption that module memory
is writable when STRICT_MODULE_RWX is disabled, for instance for kernel
debuggin.

Only enable ROX cache in execmem when STRICT_MODULE_RWX is set to
restore the original behaviour of module text permissions.

Fixes: 64f6a4e1 ("x86: re-enable EXECMEM_ROX support")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20250603111446.2609381-3-rppt@kernel.org