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/chromebook_jerry_defconfig b/configs/chromebook_jerry_defconfig
index bc7f0d2..5335aa5 100644
--- a/configs/chromebook_jerry_defconfig
+++ b/configs/chromebook_jerry_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_SPL_I2C_SUPPORT=y
 # CONFIG_SPL_MMC_SUPPORT is not set
+CONFIG_SPL_POWER_SUPPORT=y
 CONFIG_ROCKCHIP_RK3288=y
 CONFIG_TARGET_CHROMEBOOK_JERRY=y
 CONFIG_ROCKCHIP_FAST_SPL=y