cmd/compile: combine similar code in amd64's assembly generator
cmd/compile: combine similar code in amd64's assembly generator

BSFQ/BSRQ/BSFL/BSRL/SQRTSD have similar logic in amd64's assembly
generator. This CL combines them together while does not impact
generated amd64 code. The total size of
pkg/linux_amd64/cmd/compile/internal decreases about 1.8KB.

Change-Id: I5f3210c5178c20ac9108877c69f17234baf5b6b7
Reviewed-on: https://go-review.googlesource.com/c/140438
Run-TryBot: Ben Shi <d305faf1f9df9cf68436458fcb54165e72b1642e@163.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

cloudflare/go,josharian/go,CAFxX/go,golang/go,golang/go,CAFxX/go,josharian/go,akutz/go,CAFxX/go,nawawi/go,akutz/go,akutz/go,josharian/go,CAFxX/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,josharian/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,akutz/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,josharian/go,cloudflare/go,nawawi/go,akutz/go,cloudflare/go,golang/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,josharian/go,golang/go,cloudflare/go,josharian/go,akutz/go