syscall: support Linux syscalls without error return on mipsx/mips64x

Like on other architectures, use rawSyscallNoError for Linux syscalls
that don't return an error and convert all applicable occurences of
RawSyscall to use it instead.

This was missed in CL 84485 because mkall.sh doesn't support
mipsx/mips64x, so add the corresponding entries as well.

Updates #22924

Change-Id: I762cbee0827140b9890c4a10830e0b4cd33de92f
Reviewed-on: https://go-review.googlesource.com/118655


Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>