lint: Add test for whitespace issues in the code

lint: Add test for whitespace issues in the code

So far it tests for trailing whitespace.
"Upstream" files (bison/flex's .?_shipped, kconfig, vendorcode) are ignored.

Change-Id: I7af1954d537fd05f06cd210ac130dac87892159b
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/645
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>