Tegra: Change Tegra20 to Tegra in common code, prep for T30

Convert TEGRA20_ defines to either TEGRA_ or NV_PA_ where appropriate.
Convert tegra20_ source file and function names to tegra_, also.

Upcoming Tegra30 port will use common code/defines/names where possible.

Signed-off-by: Tom Warren <twarren@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
diff --git a/board/avionic-design/common/tamonten.c b/board/avionic-design/common/tamonten.c
index a0a4d1d..93f12ea 100644
--- a/board/avionic-design/common/tamonten.c
+++ b/board/avionic-design/common/tamonten.c
@@ -78,7 +78,7 @@
 	pin_mux_mmc();
 
 	/* init dev 0, SD slot, with 4-bit bus */
-	tegra20_mmc_init(0, 4, GPIO_PI6, GPIO_PH2);
+	tegra_mmc_init(0, 4, GPIO_PI6, GPIO_PH2);
 
 	return 0;
 }