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

All SPI-based device drivers needs to call SPI_HWFEATURES() with zero in order to co-exist with drivers that use H/W features