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/P1010RDB-PA_SDCARD_defconfig b/configs/P1010RDB-PA_SDCARD_defconfig
index f5769d7..3e4088b 100644
--- a/configs/P1010RDB-PA_SDCARD_defconfig
+++ b/configs/P1010RDB-PA_SDCARD_defconfig
@@ -18,6 +18,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_SPL_FRAMEWORK is not set
+CONFIG_SPL_MMC_BOOT=y
 CONFIG_SPL_TEXT_BASE=0xD0001000
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_I2C_SUPPORT=y