configs: Migrate the various SPL_BOOT_xxx choices for PowerPC

The non-CONFIG_SPL_FRAMEWORK SPL used on some PowerPC platforms have a
choice between CONFIG_SPL_NAND_BOOT, CONFIG_SPL_MMC_BOOT and
CONFIG_SPL_SPI_BOOT.  Migrate this to Kconfig

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P1022DS_SPIFLASH_defconfig b/configs/P1022DS_SPIFLASH_defconfig
index f4e4e0e..7696298 100644
--- a/configs/P1022DS_SPIFLASH_defconfig
+++ b/configs/P1022DS_SPIFLASH_defconfig
@@ -17,6 +17,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_SPL_FRAMEWORK is not set
+CONFIG_SPL_SPI_BOOT=y
 CONFIG_SPL_TEXT_BASE=0xf8f81000
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_I2C_SUPPORT=y