Xtensa ESP32: Some fixes from integration of ostest configuration.  Almost works: There are some assertions in xtensa_sigdeliver()

Xtensa ESP32:  Clock frequency is different if running from IRAM or is booting from FLASH.   This is a booltloader issue.

Support PWM_PULSECOUNT feature for TI tiva

Xtensa ESP32: Need to spill registers to memory as the last dying action before switching to a new thread.

Fix context save logic when called in window ABI configuration. Add an IDLE stack.  Don't depend on the mystery stack received from the bootloader.