include/, sched/, and libc/: Add support for sporadic scheduling parameters in struct sched_param, posix_spawnattr_t, and pthread_attr_t. Update all user interfaces to pass sporadic scheduling parameters.  Feature is dependent on EXPERIMENTAL and no changes have yet been made to core scheduling logic.

pthread_create: Fix an (unlikely) error in fallback value in the event of a failure (which should never occur)

TCB: Increase the size of the scheduling policy field from 1 to 2 bits to allow additional, planned scheduling policies

Fix a warning detected by tools/tesbuild.sh.  function was not returning the correct value in the case of errors

Syscall fixes: Add support for Cortex-M7; mount syscall has to be suppressed if there are no mountable file systems

Correct some problems with SAM3/4 watchdog driver.  Includes some small improvements.  From Max Neklyudov.

drvers/sensor and include/nuttx/sensors: Add support to Bosch BMP180 barometer.  From Alan Carvalho de Assis.

STM32 F7 Ethernet:  Add cache operations to make sure we have data coherency when accessing all DMA-related data