Add support for the STM32152 and STM32162 Medium+ density parts (plus miscellaneous other improvements to the original STM32151 logic).  From Jussi Kivilinna and Sami Pelkonen

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

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