Remove no-op Makefiles under mainboard directory

Remove no-op Makefiles under mainboard directory

Patch removes following files:

    src/mainboard/amd/serengeti_cheetah/Makefile.inc
    src/mainboard/amd/serengeti_cheetah_fam10/Makefile.inc
    src/mainboard/broadcom/blast/Makefile.inc
    src/mainboard/hp/dl145_g1/Makefile.inc
    src/mainboard/msi/ms9282/Makefile.inc
    src/mainboard/supermicro/h8dme/Makefile.inc
    src/mainboard/tyan/s2881/Makefile.inc
    src/mainboard/tyan/s2892/Makefile.inc
    src/mainboard/via/epia-m700/Makefile.inc

Change-Id: I020776313abff1772be38afc896af51ca5ab6453
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/612
Tested-by: build bot (Jenkins)
Reviewed-by: Kerry Sheh <shekairui@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>