Consolidate Linux readahead implementation

This patch consolidate Linux readahead implementation on generic
sysdeps/unix/sysv/linux/readahead.c one.  The changes are:

  - Assume __NR_readahead existence with current minimum kernel of 3.2
    for all architectures.

  - Use INLINE_SYSCALL_CALL, __ALIGNMENT_ARG, and SYSCALL_LL64 to pass
    the 64 bit offset.  This allows architectures with different abis
    to use the same implementation.

  - Remove arch-specific readahead implementations.

Checked on x86_64-linux-gnu and i686-linux-gnu.

	* sysdeps/unix/sysv/linux/arm/readahead.c: Remove file.
	* sysdeps/unix/sysv/linux/mips/mips32/readahead.c: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n32/syscalls.list (readahead):
	Remove.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/readahead.c (__readahead): Assume
	__NR_readahead existence, and use INLINE_SYSCALL_CALL, __ALIGNMENT_ARG,
	and SYSCALL_LL64.

sysdeps/unix/sysv/linux/mips/mips32/readahead.c

@@ -1 +0,0 @@
-#include <sysdeps/unix/sysv/linux/arm/readahead.c>

sysdeps/unix/sysv/linux/mips/mips64/n32/syscalls.list

@@ -4,8 +4,6 @@
 # return value.
 lseek64		-	lseek		i:iii	__lseek64	__libc_lseek64 lseek64 llseek
 
-readahead	-	readahead	i:iii	__readahead	readahead
-
 prlimit64	EXTRA	prlimit64	i:iipp	prlimit64
 
 fanotify_mark	EXTRA	fanotify_mark	i:iiiis	fanotify_mark

sysdeps/unix/sysv/linux/mips/mips64/n64/syscalls.list

@@ -1,7 +1,5 @@
 # File name	Caller	Syscall name	# args	Strong name	Weak names
 
-readahead	-	readahead	i:iii	__readahead	readahead
-
 prlimit		EXTRA	prlimit64	i:iipp	prlimit		prlimit64
 
 fanotify_mark	EXTRA	fanotify_mark	i:iiiis	fanotify_mark