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/zynq_cc108_defconfig b/configs/zynq_cc108_defconfig
index d328fe6..170cfbd 100644
--- a/configs/zynq_cc108_defconfig
+++ b/configs/zynq_cc108_defconfig
@@ -12,6 +12,7 @@
 CONFIG_BOOTCOMMAND="run $modeboot || run distro_bootcmd"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SPL_STACK_R=y
+CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_PROMPT="Zynq> "
 CONFIG_CMD_DFU=y
 # CONFIG_CMD_FLASH is not set