Convert CONFIG_SPL_PAD_TO et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_PAD_TO
   CONFIG_SPL_MAX_SIZE
   CONFIG_TPL_PAD_TO
   CONFIG_TPL_MAX_SIZE

Note that we need to make TPL_MAX_SIZE be hex, and so move and convert the
existing places.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/elgin-rv1108_defconfig b/configs/elgin-rv1108_defconfig
index 113b7c8..8a57c15 100644
--- a/configs/elgin-rv1108_defconfig
+++ b/configs/elgin-rv1108_defconfig
@@ -19,6 +19,7 @@
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_LATE_INIT=y
+CONFIG_SPL_PAD_TO=0x7f8000
 CONFIG_CMD_GPIO=y
 CONFIG_RANDOM_UUID=y
 CONFIG_CMD_MMC=y