Beginning updates of SAM3U header files o include support for the SAM4S: WDT, SUPC, EEFC, MATRIX, and PMC

SAM4L: Add logic to enable selected peripherals on power up; Extend configuration so that each peripheral can be selected -- even though the drivers are not yet implemented

Fix a backward conditional that cause the STM32 usb host driver to fail to detect disconnection events.  From Scott

Add flow control support to the STM32 serial driver; Fix some issues with UART2 and 5.  From Lorenz Meier and Mike Smith

Add register definitions for SAM4L BPM and SCIF blocks; SAM4L clock initialization now selects an optimal  power scaling mode

If CONFIG_STM32_DMACAPABLE is defined, use stm32_dmacapable to workaround attempt SPI DMAs from the CCM stack