u-boot: Move recipes to the Aspeed BSP layer

Move the u-boot recipes out of the Phosphor layer to the Aspeed layer.
When a SOC requires a specific u-boot tree, convention dictates the
BSP layer supporting the SOC includes recipes for that tree.

Tested: Built image and verified in witherspoon qemu
Change-Id: I4d5bade05566ae4cbcf5a2c637a1ed275c63ab36
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
3 files changed