kconfig: Disable 'RETPOLINE' on unsupported platforms

RETPOLINE has been enabled by default on most platforms, but it is
only supported on X86.

Features should only be enabled if they are supported and active on
the given platform. To rectify this we have RETPOLINE depend on X86,
the only platform on which it is implemented.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>
1 file changed