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/cm_t43_defconfig b/configs/cm_t43_defconfig
index fadf65d..917bd6a 100644
--- a/configs/cm_t43_defconfig
+++ b/configs/cm_t43_defconfig
@@ -23,6 +23,7 @@
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_MTD_SUPPORT=y
 CONFIG_SPL_POWER_SUPPORT=y
+CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_PROMPT="CM-T43 # "
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_EEPROM=y