aspeed: Add Aspeed global configuration file

Create a common Aspeed layer configuration file to host pointers to
things like u-boot and kernel trees that support SOCs from Aspeed.

Tested: Built image and verified in witherspoon qemu
Change-Id: I9ad2720d8b4dff191e43be0b2c1514d25d7bf3ef
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
3 files changed