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/P1020RDB-PC_defconfig b/configs/P1020RDB-PC_defconfig
index 069a35f..36472f7 100644
--- a/configs/P1020RDB-PC_defconfig
+++ b/configs/P1020RDB-PC_defconfig
@@ -21,6 +21,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_MISC_INIT_R is not set
+CONFIG_SPL_MAX_SIZE=0x20000
 CONFIG_SPL_FLUSH_IMAGE=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_AUTO_COMPLETE is not set