STM32 RTC: Add retry to initialization logic.  Sometime RTC initialization takes longer.  From dlsitzer.

Make sure that all references to up_prioritize_irq() are conditioned on CONFIG_ARCH_IRQPRIO.  Noted by Make Smith

Add an alternate STM32 I2C driver that works around errata in the F103 chip (and maybe others).  From Patrizio Simona

STM32 I2C: Bring in PX4 fix for I2C in very high noise environments or with rogue perpipherals.  Taken from the PX4 commit by Tridge

Couple of fixes for the latest STM32 additions / modifications.  These are simple fixes dealing with conditional compile based on CONFIG items not being set.  From Ken Pettit

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

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

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

STM32:  More places where up_prioritize_irq is called when CONFIG_ARCH_IRQPRIO is not defined.  Sourceforge ticket #26