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/board/nvidia/common/board.c b/board/nvidia/common/board.c
index afe832a..8821fdf 100644
--- a/board/nvidia/common/board.c
+++ b/board/nvidia/common/board.c
@@ -25,20 +25,19 @@
 #include <ns16550.h>
 #include <linux/compiler.h>
 #include <asm/io.h>
-#include <asm/arch/tegra20.h>
-#include <asm/arch/sys_proto.h>
-
-#include <asm/arch/board.h>
-#include <asm/arch/clk_rst.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/emc.h>
 #include <asm/arch/pinmux.h>
-#include <asm/arch/pmc.h>
 #include <asm/arch/pmu.h>
-#include <asm/arch/uart.h>
-#include <asm/arch/warmboot.h>
-#include <spi.h>
+#include <asm/arch/tegra.h>
 #include <asm/arch/usb.h>
+#include <asm/arch-tegra/board.h>
+#include <asm/arch-tegra/clk_rst.h>
+#include <asm/arch-tegra/pmc.h>
+#include <asm/arch-tegra/sys_proto.h>
+#include <asm/arch-tegra/uart.h>
+#include <asm/arch-tegra/warmboot.h>
+#include <spi.h>
 #include <i2c.h>
 #include "board.h"
 #include "emc.h"