cmd/compile/internal/ssa: add Op{SP,SB} type checks to check.go

gc/ssa.go initilizes SP and SB values with TUINTPTR type.
Assign same type in SSA tests and modify check.go to catch
mismatching types for those ops.

This makes SSA tests more consistent.

Change-Id: I798440d57d00fb949d1a0cd796759c9b82a934bd
Reviewed-on: https://go-review.googlesource.com/106658


Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>