This converts the following to Kconfig:
   CONFIG_SYS_SPI_U_BOOT_OFFS
Signed-off-by: NHannes Schmelzer <hannes.schmelzer@br-automation.com>
[trini: Expose this for SPL_SPI_SUNXI for now]
Signed-off-by: NTom Rini <trini@konsulko.com>