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().

EFM32: Rename efm_spi_initialize to efm_spibus_initialize for compatibility with corresponding changes to other platforms