Tegra: assembly version of the 'plat_core_pos_by_mpidr' handler

The 'plat_core_pos_by_mpidr' handler gets called very early during boot
and the compiler generated code overwrites the caller's registers.

This patch converts the 'plat_core_pos_by_mpidr' handler into an assembly
function and uses registers x0-x3, to fix this anomaly.

Change-Id: I8d974e007a0bad039defaf77b11a180d899ead3c
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
diff --git a/plat/nvidia/tegra/common/tegra_common.mk b/plat/nvidia/tegra/common/tegra_common.mk
index 50c9592..66d037f 100644
--- a/plat/nvidia/tegra/common/tegra_common.mk
+++ b/plat/nvidia/tegra/common/tegra_common.mk
@@ -32,5 +32,4 @@
 				${COMMON_DIR}/tegra_io_storage.c		\
 				${COMMON_DIR}/tegra_platform.c			\
 				${COMMON_DIR}/tegra_pm.c			\
-				${COMMON_DIR}/tegra_sip_calls.c			\
-				${COMMON_DIR}/tegra_topology.c
+				${COMMON_DIR}/tegra_sip_calls.c