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/arch/arm/cpu/tegra-common/timer.c b/arch/arm/cpu/tegra-common/timer.c
index 562e414..034ea5a 100644
--- a/arch/arm/cpu/tegra-common/timer.c
+++ b/arch/arm/cpu/tegra-common/timer.c
@@ -37,8 +37,8 @@
 
 #include <common.h>
 #include <asm/io.h>
-#include <asm/arch/tegra20.h>
-#include <asm/arch/timer.h>
+#include <asm/arch/tegra.h>
+#include <asm/arch-tegra/timer.h>
 
 DECLARE_GLOBAL_DATA_PTR;