The Intel Gateway reset controller is only present on Intel Gateway
platforms.  Hence add a dependency on X86, to prevent asking the user
about this driver when configuring a kernel without Intel Gateway
support.

Fixes: c9aef213 ("reset: intel: Add system reset controller driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>