[MC] Make MCStreamer aware of AsmParser's StartTokLoc

A SMLoc allows MCStreamer to report location-aware diagnostics, which
were previously done by adding SMLoc to various methods (e.g. emit*) in an ad-hoc way.

Since the file:line is most important, the column is less important and
the start token location suffices in many cases, this patch reverts
b7e7131a

```
// old
symbol-binding-changed.s:6:8: error: local changed binding to STB_GLOBAL
.globl local
       ^
// new
symbol-binding-changed.s:6:1: error: local changed binding to STB_GLOBAL
.globl local
^
```

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D90511