Add environment variables for SMC and SC port paths

Change-Id: I1fd734be1f42acdf7ec0c01710d585c7ca002431

platforms/nexus/setup.sh

diff --git a/platforms/nexus/setup.sh b/platforms/nexus/setup.sh
index 53fc866..61951c0 100644
--- a/platforms/nexus/setup.sh
+++ b/platforms/nexus/setup.sh
@@ -127,6 +127,9 @@
     # TODO(b/316200811) track down all the places we use a different variable name:
     export NEXUS_BOARD="${nexus_id}"
     export FPGA_BOARD_ID="${nexus_id}"
+
+    export SMC_UART="/dev/Nexus-CP210-FPGA-UART-${NEXUS_ID}"
+    export SC_UART="/dev/Nexus-FTDI-${NEXUS_ID}-FPGA-UART"
 }
 
 function opentitantool

platforms/sparrow/setup.sh

diff --git a/platforms/sparrow/setup.sh b/platforms/sparrow/setup.sh
index e8fb481..6bebc9d 100644
--- a/platforms/sparrow/setup.sh
+++ b/platforms/sparrow/setup.sh
@@ -124,6 +124,8 @@
     fi
 
     export SPARROW_ID="${sparrow_id}"
+    export SMC_UART="/dev/Sparrow-${SPARROW_ID}-SMC-UART"
+    export SC_UART="/dev/Sparrow-${SPARROW_ID}-SECURE-UART"
 }
 
 function opentitantool