Consolidate pread/pread64 implementations

This patch consolidates all the pread/pread64 implementation for Linux
in only one (sysdeps/unix/sysv/linux/pread.c).  It also removes the
syscall from the auto-generation using assembly macros.

For pread{64} offset argument placement the new SYSCALL_LL{64} macro
is used.  For pread ports that do not define __NR_pread will use
__NR_pread64 and for pread64 ports that dot define __NR_pread64 will
use __NR_pread for the syscall.

Checked on x86_64, x32, i386, aarch64, and ppc64le.

	* sysdeps/unix/sysv/linux/arm/pread.c: Remove file.
	* sysdeps/unix/sysv/linux/arm/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/pread.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/pread.c: Likewise,
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/syscalls.list (pread): Remove
	syscall generation.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
	[__NR_pread64] (__NR_pread): Remove define.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h:
	[__NR_pread64] (__NR_pread): Likewise.
	* sysdeps/unix/sysv/linux/pread.c [__NR_pread64] (__NR_pread): Remove
	define.
	(__libc_pread): Use SYSCALL_LL macro on offset argument.
	* sysdeps/unix/sysv/linux/pread64.c [__NR_pread64] (__NR_pread):
	Remove define.
	(__libc_pread64): Use SYSCALL_LL64 macro on offset argument.
	* sysdeps/unix/sysv/linux/sh/pread.c: Rewrite using default
	Linux implementation as base.
	* sysdeps/unix/sysv/linux/sh/pread64.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/pread.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/pread64.c: Likewise.

sysdeps/unix/sysv/linux/mips/kernel-features.h

@@ -39,4 +39,5 @@
    pass 64-bits values through syscalls.  */
 #if _MIPS_SIM == _ABIN32
 # define __ASSUME_WORDSIZE64_ILP32	1
+# define __ASSUME_OFF_DIFF_OFF64        1
 #endif