Linux port for Xtensa

Phase 1

Goal: linux mainline contains the latest linux-xtensa updates, builds and works.

compilable with latest GCC

overlays to cover: FSF, dc232b, more TBD

tests to pass: builds, boots, LTP

boards to focus on: ISS, ML605

configurations: UP, linux-next specific, more TBD

Plan

Prepare for linux-next participation

[2/3] Make mainline build for ARCH=xtensa in defconfig, allnoconfig, allmodconfig

fix remaining issues with allmodconfig

what with GPIO?

[+] try other fix for literals.unlikely

why there's no simdisk in the mainline?

[+] Make built images work (qemu, FSF and dc232b)

Build userspace

Analyse reference tree