spl: Migrate SYS_SATA_FAT_BOOT_PARTITION to Kconfig

This moves SYS_SATA_FAT_BOOT_PARTITION to Kconfig and enforces the
current default via Kconfig rather than C code.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index fef01bd..c6da4a4 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1232,6 +1232,11 @@
 	  expense and power consumption. This enables loading from SATA
 	  using a configured device.
 
+config SYS_SATA_FAT_BOOT_PARTITION
+	int "Partition on the SATA disk to load U-Boot from"
+	depends on SPL_SATA && SPL_FS_FAT
+	default 1
+
 config SPL_SATA_RAW_U_BOOT_USE_SECTOR
 	bool "SATA raw mode: by sector"
 	depends on SPL_SATA