test/codegen: simplify asmcheck pattern matching

Separate patterns in asmcheck by spaces instead of commas.
Many patterns end in comma (like "MOV [$]123,") so separating
patterns by comma is not great; they're already quoted, so spaces are fine.

Also replace all tabs in the assembly lines with spaces before matching.
Finally, replace \$ or \\$ with [$] as the matching idiom.
The effect of all these is to make the patterns look like:

  	   // amd64:"BSFQ" "ORQ [$]256"

instead of the old:

  	   // amd64:"BSFQ","ORQ\t\\$256"

Update all tests as well.

Change-Id: Ia39febe5d7f67ba115846422789e11b185d5c807
Reviewed-on: https://go-review.googlesource.com/c/go/+/716060
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>

test/codegen/schedule.go

@@ -8,8 +8,8 @@ package codegen
 
 func f(n int) int {
 	r := 0
-	// arm64:-"MOVD\t R"
-	// amd64:-"LEAQ","INCQ"
+	// arm64:-"MOVD  R"
+	// amd64:-"LEAQ" "INCQ"
 	for i := range n {
 		r += i
 	}