posix_fadvise.2, pread.2, readahead.2, sync_file_range.2, truncate.2: Refer to syscal...

posix_fadvise.2, pread.2, readahead.2, sync_file_range.2, truncate.2: Refer to syscall(2) for ABI semantics on certain 32-bit architectures

Also: in sync_file_range.2 and posix_fadvise.2 remove description
of conventional calling signature as flawed, and in
posix_fadvise.2, de-emphasize focus on ARM, and rather phrase
as a more general discussion of certain architectures.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>