[X86] Update RET/LRET instruction to use the same naming convention as IRET (PR36876). NFC

Be more consistent in the naming convention for the various RET instructions to specify in terms of bitwidth.

Helps prevent future scheduler model mismatches like those that were only addressed in D44687.

Differential Revision: https://reviews.llvm.org/D113302
diff --git a/llvm/test/DebugInfo/X86/dbg_value_list_emission.mir b/llvm/test/DebugInfo/X86/dbg_value_list_emission.mir
index e3380cb..e447fa8 100644
--- a/llvm/test/DebugInfo/X86/dbg_value_list_emission.mir
+++ b/llvm/test/DebugInfo/X86/dbg_value_list_emission.mir
@@ -97,5 +97,5 @@
     ; CHECK-NEXT:   DW_AT_name ("localh")

     ; CHECK-NOT:   DW_AT_location

 

-    RETQ debug-location !15

+    RET64 debug-location !15

 ...