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/sama5d3xek_spiflash_defconfig b/configs/sama5d3xek_spiflash_defconfig
index 453b16b..b27a288 100644
--- a/configs/sama5d3xek_spiflash_defconfig
+++ b/configs/sama5d3xek_spiflash_defconfig
@@ -29,6 +29,7 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SPL_TEXT_BASE=0x300000
 CONFIG_SPL_SPI_LOAD=y
+CONFIG_SYS_SPI_U_BOOT_OFFS=0x10000
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set