[ARM] Use GenericTable PrimaryKey to remove one of the SearchIndexes for BankedRegsList. NFC

Author: topperc

llvm/lib/Target/ARM/ARMSystemRegister.td

@@ -154,18 +154,16 @@ class BankedReg<string name,  bits<8> enc> {
 def BankedRegsList : GenericTable {
   let FilterClass = "BankedReg";
   let Fields = ["Name", "Encoding"];
+
+  let PrimaryKey = ["Encoding"];
+  let PrimaryKeyName = "lookupBankedRegByEncoding";
 }
 
 def lookupBankedRegByName : SearchIndex {
   let Table = BankedRegsList;
   let Key = ["Name"];
 }
 
-def lookupBankedRegByEncoding : SearchIndex {
-  let Table = BankedRegsList;
-  let Key = ["Encoding"];
-}
-
 
 // The values here come from B9.2.3 of the ARM ARM, where bits 4-0 are SysM
 // and bit 5 is R.