Tiva SSI: Fix oversight in last commit.  Would only fixe the case where the single SSI enabled was SSI0

Tiva SSI: Fix some recent breakage to the Tiva SSI driver for the case where only one SSI modules is enabled

Serial:  Allow serial console selection even if /dev/console is disabled:  There can still be a serial console with no file system at all

Semaphores:  sem_waitirq.c must be built when signals are disabled.  That is because not handles not only the case of semaphore wait being awakened by a signal, but also the case with sem_timedwait.c when the semaphore wait is awakened by a timeout.

Remove STM32-specific RX flow control logic from the upper level serial driver to the lower level STM32 serial driver

Serial RX Flow Control:  Fix a bunch of compile problems introduced into unbuilt, conditioned out logic