ANDROID: unconditionally compile sig_ok in struct module

The generic kernel image must have module signing disabled so it can
load kernel modules from all vendors. Unfortunately loading a signed
kernel module into a kernel with module signing disabled will fail
because struct module_layout (which appears in kernel modules) contains
struct module, and struct module contains the sig_ok field, which is
conditionally compiled depending on CONFIG_MODULE_SIG (module signing).

Unconditionally compile the sig_ok field to work around this problem.

Bug: 135940219
Test: load a signed kernel module with module signing disabled
Change-Id: I5cc437c806f74f89c0e45ce4135136ca0c70738e
Signed-off-by: Steve Muckle <smuckle@google.com>