Tegra20: Move some include files to arch-tegra for sharing with Tegra30

The move is pretty straight-forward. ap20.h and tegra20.h were renamed to ap.h and tegra.h.
Some files remain in arch-tegra20 but 'include' a file in 'arch-tegra' with #defines & structs
that will be common between T20 and T30 HW. HW-specific #defines, etc. stay in the 'arch-tegra20'
'root' file.

All boards build OK w/MAKEALL -s tegra20. Checkpatch.pl runs clean. Seaboard works OK.

Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/include/configs/tegra20-common.h b/include/configs/tegra20-common.h
index e213375..41fc0cb 100644
--- a/include/configs/tegra20-common.h
+++ b/include/configs/tegra20-common.h
@@ -36,7 +36,7 @@
 
 #define CONFIG_SYS_CACHELINE_SIZE	32
 
-#include <asm/arch/tegra20.h>		/* get chip and board defs */
+#include <asm/arch/tegra.h>		/* get chip and board defs */
 
 /*
  * Display CPU and Board information