xtensa: Zephyr SDK build and emulation support

[zephyrbot]

Reported by Andrew Boie:

We need a build of GCC and QEMU in our SDK and a board target defined that successfully runs zephyr cases in sanitycheck under QEMU. Although anyone serious about Xtensa will be using Cadence's tools, we need to be able to run our kernel object tests in sanitycheck with the SDK, so that users of other arches will know if they accidentally break Xtensa. We need our CI to be testing Xtensa as well.

(Imported from Jira ZEP-1731)