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/topic_miamiplus_defconfig b/configs/topic_miamiplus_defconfig
index dffc04e..39cdb22 100644
--- a/configs/topic_miamiplus_defconfig
+++ b/configs/topic_miamiplus_defconfig
@@ -13,6 +13,7 @@
 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-uboot> "
 CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_MEMTEST=y