ARM: Overhaul the ARM Makefile.

The ARM Makefile was copied from x86 and then modified, and as a result it
was carrying a lot of baggage. On top of that, the extra complication made it
inflexible, and we need a lot of flexiblity in order to support the fact that
the Tegra124 starts on an ARMv4 coprocessor instead of one of the ARMv7 main
CPUs.

Change-Id: Ia6ddc27619bdb51e152ad0c628ad6f3037c103ce
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/171017
Reviewed-by: Ronald Minnich <rminnich@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 512d942788336c8d52470135b43ee4e6a1c95f6c)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6709
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: David Hendricks <dhendrix@chromium.org>

src/soc/nvidia/tegra124/bootblock.c

@@ -17,7 +17,8 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-void bootblock_cpu_init(void);
+#include <bootblock_common.h>
+
 void bootblock_cpu_init(void)
 {
 }