meta-aspeed: Set SOC_FAMILY in SoC include files

Set SOC_FAMILY to aspeed-g4 and aspeed-g5 in ast2400 and ast2500 SoC
include files, respectively.
Include soc-family.inc so that the family is added to MACHINEOVERRIDES.
This is just minor cleanup that helps set the scene for creating Aspeed
model-specific include files (though I don't plan to do this).

Tested: Inspected OVERRIDES with the bb utility. MACHINEOVERRIDES for
witherspoon is now "openbmc:armv6:aspeed-g5:witherspoon:ast2500".
Signed-off-by: Xo Wang <xow@google.com>
Change-Id: I4175915b750b04f36e7b3bd354a55b6a4f7f51fb
2 files changed