runtime, misc/cgo/test: fix build for Linux/ARM

runtime, misc/cgo/test: fix build for Linux/ARM
1. In CL 5989057, I made a mistake in the last minute change.
"MOVW.W R4, -4(SP)" should really be "MOVW.W R4, -4(R13)",
as 5l will rewrite offset for SP.
2. misc/cgo/test/issue1560.go tests for parallel sleep of 1s,
but on ARM, the deadline is frequently missed, so change sleep
time to 2s on ARM.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/6202043