Convert CONFIG_SYS_SPI_U_BOOT_OFFS to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_SPI_U_BOOT_OFFS

Signed-off-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
[trini: Expose this for SPL_SPI_SUNXI for now]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/zynq_cse_qspi_defconfig b/configs/zynq_cse_qspi_defconfig
index e12306f..4972d70 100644
--- a/configs/zynq_cse_qspi_defconfig
+++ b/configs/zynq_cse_qspi_defconfig
@@ -22,6 +22,7 @@
 # CONFIG_ARCH_EARLY_INIT_R is not set
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_SPI_LOAD=y
+CONFIG_SYS_SPI_U_BOOT_OFFS=0x100000
 # CONFIG_CMDLINE_EDITING is not set
 # CONFIG_AUTO_COMPLETE is not set
 # CONFIG_SYS_LONGHELP is not set