posix: Set p{read,write}v2 to return ENOTSUP (BZ#21780)

posix: Set p{read,write}v2 to return ENOTSUP (BZ#21780)

Different than other architectures hppa-linux-gnu define different values
for ENOTSUP and EOPNOTSUPP, where the later is a Linux specific one.
This leads to tst-preadwritev{64}v2 tests failures:

$ ./testrun.sh misc/tst-preadvwritev2
error: tst-preadvwritev2-common.c:35: preadv2 failure did not set errno to ENOTSUP (223)
error: 1 test failures

The straightforward fix is to return the POSIX defined ENOTSUP on all
p{read,write}v{64}v2 implementations instead of Linux specific one.

Checked on x86_64-linux-gnu and the tst-preadwritev{64}v2 on
hppa-linux-gnu (although due the installed kernel on my testing system
the pwritev{64}v2 with an invalid flag still fails due a known kernel
issue [1]).

	[BZ #21780]
	* sysdeps/posix/preadv2.c (preadv2): Use ENOTSUP instead of
	EOPNOTSUPP.
	* sysdeps/posix/preadv64v2.c (preadv64v2): Likewise.
	* sysdeps/posix/pwritev2.c (pwritev2): Likewise.
	* sysdeps/posix/pwritev64v2.c (pwritev64v2): Likewise.
	* sysdeps/unix/sysv/linux/preadv2.c (preadv2): Likewise.
	* sysdeps/unix/sysv/linux/preadv64v2.c (preadv64v2): Likewise.
	* sysdeps/unix/sysv/linux/pwritev2.c (pwritev2): Likewise.
	* sysdeps/unix/sysv/linux/pwritev64v2.c (pwritev64v2): Likewise.

[1] https://sourceware.org/ml/libc-alpha/2017-06/msg00726.html