z80 family: Replace explict references to g_readytorun with indirect references via the this_task() macro

EFM32, STM32, and Tiva I2C Drivers:  Clean up some kruft that is no longer needed after the last massive I2C interfcase change

ez80: Add I2C_TRANSFER method to the I2C driver; Fixes for working with ZDS-II toolchain (still some problems with internal errors; Various fixes due to bit rot

stm32_rtc_endwr(): wait for RTC_CRL_RTOFF bit to be set.  This ensures that the write "reaches" RTC registers before access is disabled by stm32_pwr_enablebkp().