platform: Add support for generic ARM platform

Add initial mosys support.

BUG=b:348095503
TEST=USE="mosys_platform_arm -mosys_platform_geralt emerge-geralt mosys
TEST=USE="mosys_platform_arm -mosys_platform_rauru emerge-rauru mosys

Change-Id: Ibff9416f4ec74c5da0f0d2d7437438dfd2331788
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/5767004
Tested-by: Yidi Lin <[email protected]>
Reviewed-by: Yu-Ping Wu <[email protected]>
Commit-Queue: Yidi Lin <[email protected]>
Reviewed-by: Jack Rosenthal <[email protected]>
4 files changed