Add opinion file for ELF and titlecase the processor name

data/languages/xtensa.ldefs

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
 <language_definitions>
-  <language processor="xtensa"
+  <language processor="Xtensa"
             endian="little"
             size="32"
             variant="default"

data/languages/xtensa.opinion

@@ -0,0 +1,6 @@
+<opinions>
+  <constraint loader="Executable and Linking Format (ELF)" compilerSpecID="default">
+    <constraint primary="94"    processor="Xtensa" size="32" variant="default"/>
+    <constraint primary="43975" processor="Xtensa" size="32" variant="default"/>
+  </constraint>
+</opinions>