unix: don't use deprecated syscalls on linux/arm64

On linux/arm64 we used to manually define syscall numbers for some
deprecated syscalls. Most of them are unused by now anyhow. Convert the
remaining syscall wrappers using them to implement the respective
functionality using a non-deprecated syscall (in the same way glibc does
it):

- Implement EpollCreate using EpollCreate1 and additionally check
  that the passed size argument is larger than 0.
- Implement Futimesat and utimes using utimensat. Also change futimesat
  on the other geese to take a string instead of *byte and let the
  generated wrapper do the BytePtrFromString conversion.
- Return ENOSYS from Ustat. The ustat syscall has been deprecated for a
  long time in favor of fstatfs and statfs. Even glibc will deprecate
  ustat in the upcoming 2.28 release [1].

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=NEWS;h=d51fa09544f03899b7ff5a80569db088c3c23c28;hb=HEAD#l90

Change-Id: I7ea38a3cd394b0875f17443b14e107fd9c70350d
Reviewed-on: https://go-review.googlesource.com/119655
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/syscall_linux_sparc64.go

@@ -68,6 +68,7 @@ func Iopl(level int) (err error) {
 	return ENOSYS
 }
 
+//sys	futimesat(dirfd int, path string, times *[2]Timeval) (err error)
 //sysnb	Gettimeofday(tv *Timeval) (err error)
 
 func Time(t *Time_t) (tt Time_t, err error) {
@@ -83,6 +84,7 @@ func Time(t *Time_t) (tt Time_t, err error) {
 }
 
 //sys	Utime(path string, buf *Utimbuf) (err error)
+//sys	utimes(path string, times *[2]Timeval) (err error)
 
 func setTimespec(sec, nsec int64) Timespec {
 	return Timespec{Sec: sec, Nsec: nsec}