Convert CONFIG_SPL_POWER_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/pengwyn_defconfig b/configs/pengwyn_defconfig
index 02b44fc..b816c70 100644
--- a/configs/pengwyn_defconfig
+++ b/configs/pengwyn_defconfig
@@ -8,12 +8,13 @@
 CONFIG_SPL_I2C_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
 CONFIG_SPL_MMC_SUPPORT=y
+CONFIG_SPL_NAND_SUPPORT=y
+CONFIG_SPL_POWER_SUPPORT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_VERSION_VARIABLE=y
 CONFIG_SPL=y
 CONFIG_SPL_ETH_SUPPORT=y
 CONFIG_SPL_MTD_SUPPORT=y
-CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_NET_SUPPORT=y
 CONFIG_SPL_NET_VCI_STRING="AM335x U-Boot SPL"
 CONFIG_HUSH_PARSER=y