Relax fast register allocator related test cases; NFC

- Relex hard coded registers and stack frame sizes
- Some test cleanups
- Change phi-dbg.ll to match on mir output after phi elimination instead
  of going through the whole codegen pipeline.

This is in preparation for https://reviews.llvm.org/D52010
I'm committing all the test changes upfront that work before and after
independently.

llvm-svn: 345532
diff --git a/llvm/test/CodeGen/ARM/fp16-instructions.ll b/llvm/test/CodeGen/ARM/fp16-instructions.ll
index eb5ec5e..6505d2b 100644
--- a/llvm/test/CodeGen/ARM/fp16-instructions.ll
+++ b/llvm/test/CodeGen/ARM/fp16-instructions.ll
@@ -1043,7 +1043,7 @@
 
 ; CHECK-SPILL-RELOAD-LABEL: fn1:
 ; CHECK-SPILL-RELOAD:       vstr.16 s0, [sp, #{{.}}]  @ 2-byte Spill
-; CHECK-SPILL-RELOAD-NEXT:  bl  fn2
+; CHECK-SPILL-RELOAD:  bl  fn2
 ; CHECK-SPILL-RELOAD-NEXT:  vldr.16 s0, [sp, #{{.}}]  @ 2-byte Reload
 }