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/mt7629_rfb_defconfig b/configs/mt7629_rfb_defconfig
index 80e5308..b1f528b 100644
--- a/configs/mt7629_rfb_defconfig
+++ b/configs/mt7629_rfb_defconfig
@@ -22,6 +22,7 @@
 CONFIG_DEFAULT_FDT_FILE="mt7629-rfb"
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_SPL_MAX_SIZE=0x10000
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_NOR_SUPPORT=y