coreboot classes: Add dynamic classes to coreboot

Provide functionality to create dynamic classes based on program name and
architecture for which the program needs to be compiled/linked. define_class
takes program_name and arch as its arguments and adds the program_name to
classes-y to create dynamic class. Also, compiler toolset is created for the
specified arch. All the files for this program can then be added to
program_name-y += .. Ensure that define_class is called before any files are
added to the class. Check subdirs-y for order of directory inclusion.

One such example of dynamic class is rmodules. Multiple rmodules can be used
which need to be compiled for different architectures. With dynamic classes,
this is possible.

Change-Id: Ie143ed6f79ced5f58c200394cff89b006bc9b342
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: http://review.coreboot.org/6426
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
northbridge/intel/*/gma.c: Remove dead code

Remove some dead coded spotted in Clang builds.

Change-Id: Ia23e16eae76593eee249e0894ef1d704a274616f
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6130
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>