Zephyr drivers for SPI and GPIO were updated recently to allow ARC to directly access GPIO including AON_GPIO and SPI. You do not need x86 at all.
Please see the updated driver and sample app for BMI160 (top of the free, master).
From: Mahendravarman Rajarao (RBEI/EAA3) [mailto:Mahendravarman.Rajarao@in.bosch.com]
Sent: Tuesday, January 3, 2017 4:24 AM
Subject: [devel] reg: Routing SPI signals connected from x86 core to the Arc core
We have connected an Accelerometer to the x86 core of C1000 (Quark_se) through SPI interface.
Interrupt line of accelerometer is also connected to the AON_GPIO_3
Now I need to route the SPI connection of x86 to Arc core. Is that possible ?
Any sample code in zephyr I can refer for this activity ?