Rename AMD_AGESA to CPU_AMD_AGESA

Rename AMD_AGESA to CPU_AMD_AGESA

Also any CPU_AMD_AGESA_FAMILYxx selects CPU_AMD_AGESA, so remove
the explicit selects from the mainboards.

Change-Id: I4d71726bccd446b0f4db4e26448b5c91e406a641
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/792
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>