Remove __ASSUME_FUTEX_LOCK_PI

Remove __ASSUME_FUTEX_LOCK_PI

This patch removes __ASSUME_FUTEX_LOCK_PI usage and assumes that
kernel will correctly return if it supports or not
futex_atomic_cmpxchg_inatomic.

Current PI mutex code already has runtime support by calling
prio_inherit_missing and returns ENOTSUP if the futex operation fails
at initialization (it issues a FUTEX_UNLOCK_PI futex operation).

Also, current minimum supported kernel (v3.2) will return ENOSYS if
futex_atomic_cmpxchg_inatomic is not supported in the system:

kernel/futex.c:

2628 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
2629                 u32 __user *uaddr2, u32 val2, u32 val3)
2630 {
2631         int ret = -ENOSYS, cmd = op & FUTEX_CMD_MASK;
[...]
2667         case FUTEX_UNLOCK_PI:
2668                 if (futex_cmpxchg_enabled)
2669                         ret = futex_unlock_pi(uaddr, flags);
[...]
2686         return ret;
2687 }

The futex_cmpxchg_enabled is initialized by calling cmpxchg_futex_value_locked,
which calls futex_atomic_cmpxchg_inatomic.

For ARM futex_atomic_cmpxchg_inatomic will be either defined (if both
CONFIG_CPU_USE_DOMAINS and CONFIG_SMP are not defined) or use the
default generic implementation that returns ENOSYS.

For m68k is uses the default generic implementation.

For mips futex_atomic_cmpxchg_inatomic will return ENOSYS if cpu has no
'cpu_has_llsc' support (defined by each chip supporte inside kernel).

For sparc, 32-bit kernel will just use default generic implementation,
while 64-bit kernel has support.

Tested on ARM (v3.8 kernel) and x86_64.

	* nptl/pthread_mutex_init.c [__ASSUME_FUTEX_LOCK_PI]
	(prio_inherit_missing): Remove define.
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	(__ASSUME_FUTEX_LOCK_PI): Likewise.
	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_FUTEX_LOCK_PI):
	Likewise.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_FUTEX_LOCK_PI): Likewise.
	* sysdeps/unix/sysv/linux/mips/kernel-features.h
	(__ASSUME_FUTEX_LOCK_PI): Likewise.
	* sysdeps/unix/sysv/linux/sparc/kernel-features.h
	(__ASSUME_FUTEX_LOCK_PI): Likewise.