Cases 27 and 28 are used to handle floating point operations, MOVW is usually
used for integer processing, and, in two cases there is code like this:
	a :=AMOVF
	if p.As == AMOVD {
	        a=AMOVD
	}
This means that MOVW was eventually replaced by MOVF, so removed MOVW from cases 27 and 28.

Change-Id: Ib438febab88058e98b569e0dfe70b8610668ee31
Reviewed-on: https://go-review.googlesource.com/c/go/+/565622


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