Delete hard-coded driver includes

Driver components are conditionally included in the build using the
Kconfig options.

Change-Id: I05417ee263a5b82e947600482dfb68f7a3f52d58
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/610
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>