This commit adds a new internal interfaces and fixes a problem with three APIs in the SMP configuration.  The new internal interface is sched_cpu_pause(tcb).  This function will pause a CPU if the task associated with 'tcb' is running on that CPU.  This allows a different CPU to modify that OS data stuctures associated with the CPU.  When the other CPU is resumed, those modifications can safely take place.

The three fixes are to handle cases in the SMP configuration where one CPU does need to make modifications to TCB and data structures on a task that could be running running on another CPU.  Those three cases are task_delete(), task_restart(), and execution of signal handles.  In all three cases the solutions is basically the same:  (1) Call sched_cpu_pause(tcb) to pause the CPU on which the task is running, (2) perform the necessary operations, then (3) call up_cpu_resume() to restart the paused CPU.

sched/clock:  Correct calculation for the case of Tickless mode with a 32-bit timer.  In that case, the calculation was returning millisecond accuracy.  That is not good when the timer accuracy is < 1 msec.

Refresh all networking configurations due to changes in work-queue related configuration variables for Ethernet drivers.

arch/:  Add option to use low-priority work queue to all Ethernet drivers in arch that support CONFIG_NET_NOINTS.

vfork(): Fix a race condition in the SMP case.  Existing logic depended on the fact that the child would not run until waitpid was called because the child had the same priority as the parent.  BUT in the SMP case that is not true... the child may run immediately on a different CPU.

Master

STM32: STM32F303xB and STM32F303xC chips have 4 ADCs

The flag is not necessary. The state of the endpoint can be determined
using 'epstate' instead.

We need to add a delay between setting and clearing the endpoint reset
bit in SAM_UDP_RSTEP. Without the delay the USB controller will (may?)
not reset the endpoint.

If the endpoint is not being reset, the Data Toggle (DTGLE) bit will
not to be cleared which will cause the next transaction to fail if
DTGLE is 1. If that happens the host will time-out and reset the bus.

Adding this delay may also fix the USBMSC_STALL_RACEWAR in
usbmsc_scsi.c, however this has not been verified yet.

Most interrupt handling logic interacts with tasks via standard mechanism such as sem_post, sigqueue, mq_send, etc.  This all call enter_critical_section and are assumed to be safe in the SMP case.

But certain logic interacts with tasks in different ways.  The only one that comes to mind are wdogs.  There is a tasking interface that to manipulate wdogs, and a different interface in the timer interrupt handling logic to manage wdog expirations.

In the normal case, this is fine.  Since the tasking level code calls enter_critical_section, interrupts are disabled an no conflicts can occur.  But that may not be the case in the SMP case.  Most architectures do not permit disabling interrupts on other CPUs so enter_critical_section must work differently:  Locks are required to protect code.

So this change adds locking (via enter_critical section) to wdog expiration logic for the the case if the SMP configuration.

drivers/net:  Add option to use low-priority work queue to all drivers in drivers/net.  Not yet added to all architecture-specific network drivers.

Timerfixes

SMP: irq_csection() has a bad assumption.  It assumed that the state of certain variables.  That was true on entry into the interrupt handler, but might change to the execution of logic within the interrupt handler.