SMP: Add spin_trylock().  Use this in conditions where other CPUs need to stopped but we cannot call enter_critical_section.

sam4s-xplained-pro/nsh: Configuration uses old, improper timer timer interface.  CONFIG_TIMER disabled in configuration.>>

SMP: Add logic to avoid a deadlock condition when CPU1 is hung waiting for g_cpu_irqlock and CPU0 is waitin for g_cpu_paused

The examples/qencoder app was trying to init the encoder by a direct call into the board, cheating in a local header to declare the normally unavailable function prototype.

Remove a assertion condition that appears to rarely cause false-alarm assertions.  Teported by Petteri Aimonen

Spinlocks:  Added capability to provide architecture-specific memory barriers.  This was for i.MX6 but does not help with the SMP problems.  It is still a good feature.