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/sama5d3xek_mmc_defconfig b/configs/sama5d3xek_mmc_defconfig
index 7428305..5074d01 100644
--- a/configs/sama5d3xek_mmc_defconfig
+++ b/configs/sama5d3xek_mmc_defconfig
@@ -34,6 +34,7 @@
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_SPL_MAX_SIZE=0x18000
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=276