spl: spi: Move CONFIG_SPL_SPI_LOAD to Kconfig

Add Kconfig entry for CONFIG_SPL_SPI_LOAD symbol and move all
configurations using it to Kconfig.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/configs/socfpga_sockit_defconfig b/configs/socfpga_sockit_defconfig
index a324666..077d5c9 100644
--- a/configs/socfpga_sockit_defconfig
+++ b/configs/socfpga_sockit_defconfig
@@ -18,6 +18,7 @@
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_STACK_R=y
+CONFIG_SPL_SPI_LOAD=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_DFU=y