Add serial method so that lower half driver can provide RX flow control information.  From Jussi Kivilinna

STM32: Fix STM32F100CB pin configuration (from Kosma Moczek); and make chip naming a little more consistent

STM32:  Add more complication to STM32 Kconfig so the correct RNG and ETHMAC options presented for the F401RE.  There are still invalid peripheral options being presented

Nucleo-F401RE:  With these changes and the changes from previous commits, the basic Nucleo-F401RE NSH configuration is working.

The Nucleo-F401RE has no on-board cystal and, hence, must use the on-chip HSI oscillator for the PLL include clock

STM32:  Add more complication to STM32 Kconfig so the correct ADC and CAN options presented for the F401RE.  There are still invalid peripheral options being presented

STM32:  Add some complication to STM32 Kconfig so the correct USART and TIM options are presented for the F401RE.  There are still invalid peripheral options being presented

SAM4S Xplained Pro: Clean-up of LED usage and also some integration of new timer features.  From Bob Doiron

The alternate console device CONFIG_NSH_CONDEV must not be defined unconditionally.  This causes errors when using Telnet sessions.  This was solved by adding CONFIG_NSH_ALTCONDEV: CONFIG_NSH_ALTCONDEV enables or disables the feature then, if enabled, CONFIG_NSH_CONDEV provides the alternative console device name

Fix configuration for F401:  It has has FSMC and so the option should not be offered.  But there are many more options available for the F401 that should be availalbe:  CAN, nonexistent timers, etc.  These will all need to be addressed

If the CPU load measurements are being driven by an external clock, then the prototype for sched_process_cpuload() must be available in include/nuttx/arch.h