mainboard/*/debug.c: Remove duplicate or dead code

We already have these implemented in 'lib/debug.c'. Will fix
'.c' includes in follow ups.

Change-Id: I1586d8864db7f93515214ef9a4458ebc618bf61c
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/7316
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>