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/sifive_unmatched_defconfig b/configs/sifive_unmatched_defconfig
index 41224d0..40aa38f 100644
--- a/configs/sifive_unmatched_defconfig
+++ b/configs/sifive_unmatched_defconfig
@@ -26,6 +26,7 @@
 CONFIG_DISPLAY_BOARDINFO=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_ID_EEPROM=y
+CONFIG_SPL_MAX_SIZE=0x100000
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_SPL_DM_RESET=y
 CONFIG_SPL_SPI_LOAD=y