nx: sepolicy: Extend UART-A/B support

* Need to explicitely allow shell to write to it, and init to
  see/interact with it.

Change-Id: I39440ed383c1fd235c38b179d3ac77883e11cf7d

sepolicy/vendor/init.te

@@ -8,4 +8,5 @@ allow init jc_setup_exec:file {execute};
 allow init permission_vendor_data_file:lnk_file relabelto;
 
 # Allow UART to function when enabled
+allow init serial_device:chr_file rw_file_perms;
 allow init tty_device:chr_file rw_file_perms;

sepolicy/vendor/shell.te

@@ -0,0 +1,2 @@
+# Allow UART to function when enabled
+allow shell serial_device:chr_file rw_file_perms;